Sin and grace may in no way coexist in the soul. (Catechism of Trent, no. 2200)

It is contrary to reason that error and truth should have equal rights. (Leo XIII. Encyclical Liberates praestantissimum, no. 34, June 20, 1888)

In fact, the remission of serious sin consists in the infusion of the sanctifying grace which has been lost, and grace is incompatible with any and every serious sin. (John Paul II. Message to the participants in the Course on the Internal Forum organized by the Apostolic Penitentiary, March 20, 1998)

The true path of the Church is fidelity to Christ. That is why the Church should persevere in ‘its truth’ and guard its ‘deposit’ in the spirit of love and for the love in which God fully reveals himself, for ‘God is love’ (Jn 4:8). It is not honestly possible to have this fidelity coexist while following other paths that distance oneself progressively from Christ and from the Church, disputing fixed points of doctrine and discipline, that, as such, have been confided to the Church and to its mandate, with the guarantee of fidelity assured by the Holy Spirit. (John Paul II. Address to the members of the Sacred College and the Roman Curia, June 28, 1980)

But the faith through which we are cleansed from sin is not ‘lifeless faith,’ which can exist even with sin, but ‘faith living’ through charity; that thus Christ’s Passion may be applied to us, not only as to our minds, but also as to our hearts. And even in this way sins are forgiven through the power of the Passion of Christ. (Saint Thomas Aquinas. Summa Theologica, III, q. 49, a. 1, ad 5)

Vice is directly contrary to virtue, even as sin to virtuous act: vice excludes virtue, just as sin excludes acts of virtue. (Saint Thomas Aquinas. Summa Theologica I-II, q. 71, a. 4)

Venial sin does not preclude every act of grace whereby all venial sins can be removed; whereas mortal sin excludes altogether the habit of grace […]. (Saint Thomas Aquinas. III, Summa Theologica, q. 87, a. 4)

The wisdom which is a gift of the Holy Ghost, as stated above (a 1), enables us to judge aright of Divine things, or of other things according to Divine rules, by reason of a certain connaturalness or union with Divine things, which is the effect of charity, as stated above (a 2; q 23, a 5). Hence the wisdom of which we are speaking presupposes charity. Now charity is incompatible with mortal sin, as shown above (q 24, a 12). Therefore it follows that the wisdom of which we are speaking cannot be together with mortal sin. (Saint Thomas Aquinas. Summa Theologica, II-II, q. 45, a. 4)

For this surely is the time of confession both for the uninitiated and for the baptized; for the one, that upon their repentance they may partake of the sacred mysteries; for the others, that having washed away their stain after baptism, they may approach the table with a clean conscience. Let us then forsake this soft and effeminate way of living. For it is not, it is not possible at once both to do penance and to live in luxury. (Saint John Chrysostom. Homilies on the Gospel of St. Matthew, 10)

To some it seems right to admit all men, without distinction, to the laver of regeneration in Christ Jesus our Lord, even though they refuse to change their evil and shameful life, noteworthy by wickedness and evidently dishonorable actions, and even declare openly that they wish to persevere in these. If someone, for instance, is linked to a harlot, he should not be first ordered to leave her and only then permitted to approach baptism, but he should be admitted and baptized even, as he professes publicly, he continues to be with her and means to so continue; that he be not hindered in becoming a member of Christ, even though he persist in being a member of the harlot (1Cor 6). Only afterwards should he be taught how great this evil, and, already baptized, he be instructed on the way to change his customs for the better. For they think it a strange and contrary to good order, that the Christian should live and then be baptized: in their opinion the Sacrament of Baptism should precede, so that the teaching on good conduct may follow. And if the baptized be willing to accept this and to observe it, it will be for his interest; but if he be unwilling, as long as still retaining the Christian Faith, without which he would perish forever, in no matter what sin or impurity he may continue, he will be saved equally, as if through fire, in the same way as one who, upon the foundation which is Christ, had built not with gold, silver and precious stones, but wood, hay and straw; that is, not with righteous and pure ways of life, but unrighteous and opposed to shame. (Saint Augustine of Hippo. On Faith and Works, no. 1)

No one should take those texts of Scripture, which imply, either as to the present or presage of the future, the mingling of the good and evil in the bosom of the Church, as if they suggest an attenuation or even a suppression of the severity of discipline or of watching, because they should consider themselves deceived by their own opinion and not instructed by these texts. (Saint Augustine of Hippo. On Faith and Works, no. 2)

When therefore the Apostle says that he judges that a man is justified through faith without the works of the law; he does not uphold this because the works of justice may be neglected once the faith has been received and professed, but so that each one may know that he may be justified by means of faith, even without having first accomplished the works of the law. […] Further, even Paul, defines as salvific and truly evangelical not any faith by which one may believe in God, but that [faith] which is preceded by the works of charity, saying: faith, which worketh through love (Gal 5:6). From which it is affirmed that the faith, which to some is sufficient for salvation, is of no avail, such that he says: If I have all faith, so as to remove mountains, and have not love, I am nothing (1 Cor 13:2). But where charity inspired by faith works, without doubt one lives well, because: the fulfillment of the law is love (Rm 13:10) (Saint Augustine of Hippo. On Faith and Works, no. 21)

James is so opposed to those who think that faith without works is useful to obtin salvation, that he compares them even with the devils. He says: Thou believest that there is One God; thou doest well: the devils also believe and tremble (Jam 2:19). What could be said that is more true and in a way that is more concise and incisive? Even in the Gospel, we read this confession when the devils proclaim Christ as the Son of God and were rebuked by Him (Mk 1:24-25), when [what they said] was praised in Peter at the profession of his faith. What will it profit, asks James, my brethren, if a man say that he hath faith, and have not works? Will faith be able to save him? (Jam 2:14). And also: faith without works is dead (Jam 2:20). How long then are they to go on being deceived, who promise themselves life everlasting on the basis of a dead faith? (Saint Augustine of Hippo. On Faith and Works, no. 23)

I do not see why the Lord would have said: If thou wilt come unto life, keep the Commandments; and recalled those which pertain to good customs (Mt 19:17-19), if it is possible to attain eternal life even without observing them, through faith alone, which without works is dead. Besides, how can it be true what He will say to them who He will set on his left hand: Go ye into everlasting fire, which is prepared for the devil and his angels? He does not rebuke them for not having believed in Him, but because they have not done good works. (Saint Augustine of Hippo. On Faith and Works, no. 25)

No less far from the truth is the dangerous error of those who endeavor to deduce from the mysterious union of us all with Christ a certain unhealthy quietism. They would attribute the whole spiritual life of Christians and their progress in virtue exclusively to the action of the Divine Spirit, setting aside and neglecting the collaboration which is due from us. (Denzinger-Hünermann 3817. Pius XII. Encyclical Mystici Corporis Christi, no. 87, June 29, 1943)

No one, of course, can deny that the Holy Spirit of Jesus Christ is the one source of whatever supernatural powers enters into the Church and its members. For ‘The Lord will give grace and glory’ as the Psalmist says. But that men should persevere constantly in their good works, that they should advance eagerly in grace and virtue, that they should strive earnestly to reach the heights of Christian perfection and at the same time to the best of their power should stimulate others to attain the same goal, – all this the heavenly Spirit does not will to effect unless they contribute their daily share of zealous activity. ‘For divine favors are conferred not on those who sleep, but on those who watch,’ as Saint Ambrose says. (Denzinger-Hünermann 3817. Pius XII. Encyclical Mystici Corporis Christi, no. 87, June 29, 1943)

The Church in posterior centuries has always followed the same path, and even today it does not proceed differently. Who does not know as our predecessor Pius X, of holy memory, amply opened to the faithful and especially to children, the doors to the Eucharistic fonts of grace? But it would be a fatal illusion to believe that the efficacy of the Holy Supper – the opus operatum – dispenses the soul from cooperation in seeking its salvation. One of the effects of the Holy Eucharist, ‘tamquam antidotum, liberemur quo en culpis quotidianis, et in peccatis mortalibus praeservemur’ (Conc. Trent, sess.13, ch.2), consists exactly in giving strength to fight against sin. The life of a Christian, which follows the example of Christ, is a life of combat against the devil, the world and the flesh. (Pius XII. Address L’inscrutabile consiglio on the Ten Commandments, February 23, 1944)

The Gospel is absolutely not a code that is easily fulfilled: it demands effort and fidelity. Here one may analyze the moral systems that renounce personal effort to obtain salvation, in the erroneous conviction that it is only by faith and only by grace that we have the fortune of being saved, without a positive and systematic moral discipline; as if faith and grace, gifts of God and true causes of salvation, do not demand a response, coherence, free and responsible cooperation on our part, either as a condition of cooperating in the saving work of God in us, or also as a consequence of the rebirth brought about by his merciful supernatural action. (Paul VI. General audience, July 7, 1971)

[Lutheran proposition condemned by Leo X] Great is the error of those who approach the sacrament of the Eucharist relying on this, that they have confessed, that they are not conscious of any mortal sin, that they have sent their prayers on ahead and made preparations; all these eat and drink judgment to themselves. But if they believe and trust that they will attain grace, then this faith alone makes them pure and worthy. (Denzinger-Hünermann 1465. Leo X, Bull Exurge Deus, June 15, 1520)

And so no one should flatter himself because of faith alone [can. 9, 19, 20], thinking that by faith alone he is made an heir and will obtain the inheritance, even though he suffer not with Christ ‘that he may be also glorified’ (Rom 8:17). (Denzinger-Hünermann 1538. Council of Trent, Session VI, January 13, 1547)

So run, that ye may obtain. Every one also who engages in the contest is temperate in all things: now these men that they may obtain a corruptible crown, but we an incorruptible. But I so run, not as uncertainty; I fight, not as One beating the air; but I make my body livid, and bring it into subjection, lest by any means, when preaching to others, I may myself be rendered a castaway. […] And the harder we strive, so much is it the more valuable; while so much the more valuable it is, so much the more should we esteem it. And indeed those things are not esteemed so highly which come spontaneously, as those which are reached by much anxious care. Since, then, this power has been conferred upon us, both the Lord has taught and the apostle has enjoined us the more to love God, that we may reach this (prize) for ourselves by striving after it. For otherwise, no doubt, this our good would be (virtually) irrational, because not the result of trial. (Saint Irenaeus. Against Heresies, Bk. 4, ch. 37, 7)

For both to prophesy and to cast out devils, and to do great acts upon the earth is certainly a sublime and an admirable thing; but one does not attain the kingdom of heaven although he is found in all these things, unless he walks in the observance of the right and just way. The Lord denounces, and says, Many shall say to me in that day, Lord, Lord, have we not prophesied in Thy name, and in Thy name have cast out devils, and in Thy name done many wonderful works? And then will I profess unto them, I never knew you: depart from me, ye that work iniquity. There is need of righteousness, that one may deserve well of God the Judge; we must obey His precepts and warnings, that our merits may receive their reward. (Saint Cyprian of Carthage. The Unity of the Church, 15)

Paul, joining righteousness to faith and weaving them together, constructs of them the breastplates for the infantrymen, armoring the soldier properly and safely on both sides. A soldier cannot be considered safely armored when either shield is disjoined the other. For faith without works of justice is not sufficient for salvation, neither however, is righteous living secure in itself of salvation, if it is disjoined from faith. (Saint Gregory of Nyssa. Homilies on Ecclesiastes, no. 8)

For, ‘think not,’ saith he [St. Paul], ‘because ye have believed, that this is sufficient for your salvation: ‘since if to me neither preaching nor teaching nor bringing over innumerable persons, is enough for salvation unless I exhibit my own conduct also unblameable , much less to you.’ (Saint John Chrysostom. Homilies on First Corinthians, 1Cor 9: 24)

The mere renunciation of sin is not sufficient for the salvation of the penitents, but also the worthy fruits of penance, which is also required of them. (Saint Basil the Great. Moralia I, 3)

Once, when I was going to Communion, I saw with the eyes of the soul, more distinctly than with those of the body, two devils of most hideous shape; their horns seemed to encompass the throat of the poor priest; and I beheld my Lord, in that great majesty of which I have spoken, held in the hands of that priest, in the Host he was about to give me. It was plain that those hands were those of a sinner, and I felt that the soul of that priest was in mortal sin. What must it be, O my Lord, to look upon Thy beauty amid shapes so hideous! Our Lord Himself told me to pray for that priest; that He had allowed this in order that I might understand the power of the words of consecration, and how God failed not to be present, however wicked the priest might be who uttered them; and that I might see His great goodness in that He left Himself in the very hands of His enemy, for my good and for the good of all. I understood clearly how the priests are under greater obligations to be holy than other persons; and what a horrible thing it is to receive this most Holy Sacrament unworthily, and how great is the devil’s dominion over a soul in mortal sin. (Saint Teresa of Jesus. The Life of Saint Teresa of Jesus, Ch. 38, no. 29-30)

We eat the body of Christ, so that we may participate in eternal life. Because what promises us a recompense and dignity, is not merely eating and drinking, but rather communion in the grace and the celestial life; and it is not the twelve thrones that were created to receive us, but it is Christ himself, who, through his identification with the divinity, judges it unnecessary to question the conduct of anyone, due to the knowledge that he has of hearts, to reward virtue and chastise the impious, and also the apostles, who received a special spiritual formation to judge, recompensing the faith and banishing false beliefs, reprehending error with vigor and persecuting the sacrilegious with holy anger. (Saint Ambrose of Milan. Treatise on the Gospel of Saint Luke, bk. 10, no. 49: ML 15, 1816)

Sacrilege is a grave sin especially when committed against the Eucharist, for in this sacrament the true Body of Christ is made substantially present for us (cf. CIC, cann. 1367; 1376.) (Catechism of the Catholic Church, no. 2120)

What hath Christ done to you? who with such exceeding patience endured His betrayer, as to give to him, as to the other Apostles, the first Eucharist consecrated with His own hands, and blessed with His own mouth. What hath Christ done to you? who sent this same betrayer, whom He called a devil, who before betraying the Lord could not show good faith even to the Lord’s purse, with the other disciples to preach the kingdom of heaven; that He might show that the gifts of God come to those that with faith receive them, though he, through whom they receive them, be such as Judas was. (Saint Augustine of Hippo. Exposition on the Book of Psalms, Psalm XI, 6)

All who even within the Church profess that they know God, but deny Him in their deeds, such as are the covetous and envious, and those who, because they hate their brethren, are pronounced to be murderers, not on my testimony, but on that of the holy Apostle John, 1 John 3:15 — all these are both devoid of hope, because they have a bad conscience; and are faithless, because they do not do what they have vowed to God; and liars, because they make false professions; and possessed of devils, because they give place in their heart to the devil and his angels; and their words work corruption, since they corrupt good manners by evil communications; and they are infidels, because they laugh at the threats which God utters against such men; and accursed, because they live wickedly; and antichrists, because their lives are opposed to Christ; and cursed of God, since holy Scripture everywhere calls down curses on such men; and dead, because they are without the life of righteousness; and unpeaceful, because by their contrary deeds they are at variance with God’s behests; and blasphemous, because by their abandoned acts despite is done to the name of Christian; and profane, because they are spiritually shut out from that inner sanctuary of God; and sacrilegious, because by their evil life they defile the temple of God within themselves; and servants of the devil, because they do service to fraud and covetousness, which is idolatry. (Saint Augustine of Hippo. On Baptism, Bk VI, Ch. 8, no. 12)

Unhappy he, who comes in to this banquet without the wedding garment (cf. Mt 22:11) of charity or penitence, because ‘he who eats unworthily, eats damnation to himself’ (cf.1Cor 11:29). What fellowship has light with darkness? (cf. 2Cor 6:14-15); Judas the traitor with the Savior? ‘The hand of him that betrayeth me is with me on the table’ (Lk22:21). It is written in Exodus: ‘Every beast,’ and therefore the man also who has made himself similar to the beasts, ‘that should touch the mountain,’ that is the body of Christ, ‘should be stoned,’ that is damned (cf. Heb 12:20; cf. Ex 19:12-13). (Saint Anthony of Padua. Sermon on the Lord’s Supper: Allegorical Sermon, 6 – English)

Shall I say something more fearful. It is not so grievous a thing for the energumens to be within, as for such as these, whom Paul affirms to trample Christ under foot, and to ‘account the blood of the covenant unclean, and to do despite to the grace of the Spirit.’ For he that hath fallen into sin and draws nigh, is worse than one possessed with a devil. For they, because they are possessed are not punished, but those, when they draw nigh unworthily, are delivered over to undying punishment. Let us not therefore drive away these only, but all without exception, whomsoever we may see coming unworthily. Let no one communicate who is not of the disciples. Let no Judas receive, lest he suffer the fate of Judas. (Saint John Chrysostom. Homily on the Gospel of Matthew, 82, 6)

For as often as you eat this bread and drink the cup, you proclaim the death of the Lord until he comes. Therefore whoever eats the bread or drinks the cup of the Lord unworthily will have to answer for the body and blood of the Lord. A person should examine himself, and so eat the bread and drink the cup. For anyone who eats and drinks without discerning the body, eats and drinks judgment on himself. (1Cor 11:26-29)

But the things that come out of the mouth come from the heart, and they defile. For from the heart come evil thoughts, murder, adultery, unchastity, theft, false witness, blasphemy. These are what defile a person. (Mt 15:18-20)

The answer is that there are two ways of receiving this sacrament, namely, spiritually and sacramentally. Therefore, some receive sacramentally and spiritually, namely, those who receive this sacrament in such a way that they also share in the reality [res] of the sacrament, namely, charity through which ecclesial unity exists. To such the Lord’s words apply: ‘He that eats me will live because of me.’ But some receive only sacramentally, namely, those who receive this sacrament in such a way that they do not have the [res] reality of the sacrament, i.e., charity. To these are applied the words spoken here: ‘He that eats and drinks unworthily eats and drinks judgment upon himself.’ Besides these two ways by which the sacrament is taken, there is a third way, by which one eats per accidens, namely, when it is taken not as a sacrament. This can happen in three ways: in one way, as when a believer receives the consecrated host, which he does not believe is consecrated: such a one has the habit of receiving this sacrament, but he does not use it actually as a sacrament. In another way, as when an unbeliever receives the consecrated host, but he has no faith about this sacrament. (Saint Thomas Aquinas. Commentary of the First Epistle to the Corinthians, lec. 7: 1Cor 11:27-34)

To recognize oneself a sinner before all, is above all to beseech God to manifest his power and his love, capable of working marvels in he who repents. (John Paul II. Homily on the Solemnity of Pentecost celebrated in the Cathedral of Brussels, July 4, 1995)

To acknowledge one’s sin, indeed-penetrating still more deeply into the consideration of one’s own personhood-to recognize oneself as being a sinner, capable of sin and inclined to commit sin, is the essential first step in returning to God. […] In effect, to become reconciled with God presupposes and includes detaching oneself consciously and with determination from the sin into which one has fallen. It presupposes and includes, therefore, doing penance in the fullest sense of the term: repenting, showing this repentance, adopting a real attitude of repentance- which is the attitude of the person who starts out on the road of return to the Father. This is a general law and one which each individual must follow in his or her particular situation. For it is not possible to deal with sin and conversion only in abstract terms. […] The first conviction is that for a Christian the sacrament of penance is the primary way of obtaining forgiveness and the remission of serious sin committed after baptism. (John Paul II. Apostolic exhortation Reconciliatio et paenitentia, nos. 13, 31)

Christ’s call to conversion continues to resound in the lives of Christians. This second conversion is an uninterrupted task for the whole Church who, ‘clasping sinners to her bosom, (is) at once holy and always in need of purification, (and) follows constantly the path of penance and renewal’ (LG 8,3). This endeavor of conversion is not just a human work. It is the movement of a ‘contrite heart,’ drawn and moved by grace to respond to the merciful love of God who loved us first (Ps 51:17; cf. Jn 6:44; 12:32; 1Jn 4:10). […] Saint Ambrose says of the two conversions that, in the Church, ‘there are water and tears: the water of Baptism and the tears of repentance’ (Saint Ambrose, ep. 41, 12) (Catechism of the Catholic Church, no. 1428. 1429)

Sin is before all else an offense against God, a rupture of communion with him. At the same time it damages communion with the Church. For this reason conversion entails both God’s forgiveness and reconciliation with the Church, which are expressed and accomplished liturgically by the sacrament of Penance and Reconciliation. (Cf. LG 11.) (Catechism of the Catholic Church, no. 1440)

Contrition, which has the first place among the aforementioned acts of the penitent, is a sorrow of the soul and a detestation of sin committed, with a determination of not sinning in the future. This feeling of contrition is, moreover, necessary at all times to obtain the forgiveness of sins, and thus for a person who has fallen after baptism it especially prepares for the remission of sins, if it is united with trust in divine mercy and with the desire of performing the other things required to receive this sacrament correctly. The holy Synod, therefore, declares that this contrition includes not only cessation from sin and a resolution and a beginning of a new life, but also hatred of the old, according to this statement: ‘Cast away from you all your transgressions, by which you have transgressed, and make to yourselves a new heart and a new spirit’ (Ez 18:31). (Denzinger-Hünermann 1676. Council of Trent, Session XIV, November 25, 1551)

For many loved their sins; many confessed their sins; and he who confesses his sins, and accuses them, does now work with God. God accuses your sins: and if you also accuse, you are united to God. There are, as it were, two things, man and sinner. That you are called man, is God’s doing; that you are called sinner, is man’s own doing. Blot out what you have done, that God may save what He has done. It behooves you to hate your own work in you, and to love the work of God in you. And when your own deeds will begin to displease you, from that time your good works begin, as you find fault with your evil works. The confession of evil works is the beginning of good works. (Saint Augustine of Hippo. Tractates on the Gospel of Saint John, Tractate 12)

This is what your God says to you: ‘Sin should be chastised either by you or by me.’ Sin is chastised either by man when he repents or by God when he judges. You are thus chastised either by yourself without yourself, or with God together with yourself. For, what is penance, if not angere against oneself? He who repents becomes angry with himself. And even the striking of the breast, if done sincerely, from where does it proceed? Why do you strike yourself if you are not angered? In this way, when you strike your breast, you are angered with your heart, and wish to satisfy your Lord. In this way also can be understood the passage of Scripture: ‘Be angered and do not sin’ (Ps 4:5). Be angered for having sinned, and chastising yourself, sin no more. ‘Awaken your heart with repentance, and it will be a sacrifice to God’ (Ps 50: 19). (Saint Augustine of Hippo. Sermon 19, no. 2)

Let us feel displeasure with ourselves when we sin, for God is displeased with sins. And since we are not free from sin, let us be similar to God at least in feeling displeasure in that which displeases him. […] God is your maker; you therefore look toward yourself and destroy in your interior that which did not come from his workshop. For – as it is written- God created man upright. (Saint Augustine of Hippo. Sermon 19, no. 4)

The same result follows from the opinions of those who assert that little importance should be given to the frequent confession of venial sins. Far more important, they say, is that general confession which the Spouse of Christ, surrounded by her children in the Lord, makes each day by the mouth of the priest as he approaches the altar of God. As you well know, Venerable Brethren, it is true that venial sins may be expiated in many ways which are to be highly commended. But to ensure more rapid progress day by day in the path of virtue, We will that the pious practice of frequent confession, which was introduced into the Church by the inspiration of the Holy spirit, should be earnestly advocated. By it genuine self-knowledge is increased, Christian humility grows, bad habits are corrected, spiritual neglect and tepidity are resisted, the conscience is purified, the will strengthened, a salutary self-control is attained, and grace is increased in virtue of the Sacrament itself. (Piux XII. Encyclical Mystici Corporis Christi, no. 88, June 29, 1943)