If you wish to enter into life, keep the commandments. (Mt 19:17)

But although Christ died for all (2Cor 5:15), yet not all receive the benefit of His death, but those only to whom the merit of His passion is communicated. For […], unless they were born again in Christ, they never would be justified [can. 2 and 10], since in that new birth through the merit of His passion, the grace, whereby they are made just, is bestowed upon them. (Denzinger-Hünermann 1523. Council of Trent, Session VI, ch. 3, Decree on Justification, January 13, 1547)

If anyone says or holds that the punishment of the demons and of impious men is temporary, and that it will have an end at some time, that is to say, there will be a complete restoration of the demons or of impious men, let him be anathema. (Denzinger-Hünermann 411. Synod of Constantinople II confirmed by Pope Vigilius, Canons against the doctrine of Origen, from the book of Emperor Justinian, 543)

Whoever wishes to be saved, needs above all to hold the Catholic faith; unless each one preserves this whole and inviolate, he will without a doubt perish in eternity. (Denzinger Hünermann 75. The Creed Quicumque, which is called ‘Athanasian’)

By the heart we believe and by the mouth we confess the one Church, not of heretics but the Holy Roman, Catholic, and Apostolic (Church) outside which we believe that no one is saved. (Denzinger-Hünermann 792. Innocent III, Profession of Faith prescribed for Durand of Osca and his Waldensian companions, December 18, 1208)

In the second place, we ask whether you and the Armenians obedient to you believe that no man of the wayfarers outside the faith of this Church, and outside the obedience of the Pope of Rome, can finally be saved. (Denzinger-Hünermann 1051. Clement VI. From the letter Super quisbusdam to the Consolator, the Catholicon of the Armenians, September 20, 1351)

It firmly believes, professes, and proclaims that those not living within the Catholic Church, not only pagans, but also Jews and heretics and schismatics cannot become participants in eternal life, but will depart ‘into everlasting fire which was prepared for the devil and his angels’ (Mt 25:41), unless before the end of life the same have been added to the flock; and that the unity of the ecclesiastical body is so strong that only to those remaining in it are the sacraments of the Church of benefit for salvation, and do fastings, almsgiving, and other functions of piety and exercises of Christian service produce eternal reward, and that no one, whatever almsgiving he has practiced, even if he has shed blood for the name of Christ, can be saved, unless he has remained in the bosom and unity of the Catholic Church. (Denzinger-Hünermann 1351, Council of Florence – Bull Cantata Domino, February 4, 1442)

Knowing that, of certain rather obscure sentences of the Apostle Paul, certain unrighteous men had taken occasion so as to be careless about a good life, as though secure of the salvation which is in faith, [St. Peter] made mention that there are certain things difficult to understand in his Epistles, which men perverted, as also they did other Scriptures, unto their own destruction. When, notwithstanding that Apostle [St. Paul] held, the same as the other Apostles, concerning eternal salvation, as what was not given except to them who live a good life. (Saint Augustine. De Fide et operibus, no. 22 – English)

The third question is one very full of danger, whence, in that it hath been little considered, and not handled according to the divine sayings, it seems to me that all that opinion hath arisen, whereby promise is made unto persons living most wicked and shameful lives, even although they go on so to live and only believe in Christ and receive His Sacraments, that they shall come unto salvation and life everlasting; in opposition to the most open sentence of the Lord, Who made answer unto him that was longing for life everlasting: ‘If thou wilt come unto life, keep the Commandments’; and made mention of what Commandments, wherein those very sins are shunned, unto which is promised, I know not how, salvation everlasting, on account of faith without works. (Saint Augustine. De Fide et operibus, no. 49 – English)

In this matter we should note that contrary causes beget contrary effects. Thus action that proceeds from malice is contrary to action that proceeds from virtue. Accordingly wretchedness, in which evil action issues, is the opposite of happiness, which virtuous action merits. Furthermore, contraries pertain to the same genus. Therefore, since final happiness, which is reached by virtuous action, is a good that belongs not to this life but to the next life, as is clear from an earlier discussion, final wretchedness, also, to which vice leads, must be an evil belonging to the next world. Besides, all goods and ills of this life are found to serve some purpose. External goods, and also bodily goods, are organically connected with virtue, which is the way leading directly to beatitude, for those who use such goods well. But for those who use these goods ill, they are instruments of vice, which ends up in misery. Similarly the ills opposed to such goods, as sickness, poverty, and the like, are an occasion of progress in virtue for some but aggravate the viciousness of others, according as men react differently to such conditions. But what is ordained to something else cannot be the final end, because it is not the ultimate in reward or punishment. Therefore neither ultimate happiness nor ultimate misery consists in the goods or ills of this life. (Saint Thomas Aquinas. Compendium of Theology, ch. 173)

The suffering of eternal punishment is in no way opposed to divine justice. Even in the laws men make, punishment need not correspond to the offense in point of time. For the crime of adultery or murder, either of which may be committed in a brief span of time, human law may prescribe lifelong exile or even death, by both of which the criminal is banned forever from the society of the state. Exile, it is true, does not last forever, but this is purely accidental, owing to the fact that man’s life is not everlasting; but the intention of the judge, we may assume, is to sentence the criminal to perpetual punishment, so far as he can. In the same way it is not unjust for God to inflict eternal punishment for a sin committed in a moment of time. We should also take into consideration the fact that eternal punishment is inflicted on a sinner who does not repent of his sin, and so he continues in his sin up to his death. And since he is in sin for eternity, he is reasonably punished by God for all eternity. (Saint Thomas Aquinas. Compendium of Theology, ch. 183)

Furthermore, any sin committed against God has a certain infinity when regarded from the side of God, against whom it is committed. For, clearly, the greater the person who is offended, the more grievous is the offense. He who strikes a soldier is held more gravely accountable than if he struck a peasant; and his offense is much more serious if he strikes a prince or a king. Accordingly, since God is infinitely great, an offense committed against Him is in a certain respect infinite; and so a punishment that is in a certain respect infinite is duly attached to it. Such a punishment cannot be infinite in intensity, for nothing created can be infinite in this way. Consequently a punishment that is infinite in duration is rightly inflicted for mortal sin. Moreover, while a person is still capable of correction, temporal punishment is imposed for his emendation or cleansing. But if a sinner is incorrigible, so that his will is obstinately fixed in sin, as we said above is the case with the damned, his punishment ought never to come to an end. (Saint Thomas Aquinas. Compendium of Theology, ch. 183)

The expression ‘for many’, while remaining open to the inclusion of each human person, is reflective also of the fact that this salvation is not brought about in some mechanistic way, without one’s own willing or participation; rather, the believer is invited to accept in faith the gift that is being offered and to receive the supernatural life that is given to those who participate in this mystery, living it out in their lives as well so as to be numbered among the ‘many’ to whom the text refers. (Letter from Cardinal Francis Arinze on the translation of ‘pro multis’, October 17, 2006)

Now We consider another abundant source of the evils with which the Church is afflicted at present: indifferentism. This perverse opinion is spread on all sides by the fraud of the wicked who claim that it is possible to obtain the eternal salvation of the soul by the profession of any kind of religion, as long as morality is maintained. Surely, in so clear a matter, you will drive this deadly error far from the people committed to your care. With the admonition of the apostle that ‘there is one God, one faith, one baptism’ (Eph 4:5) may those fear who contrive the notion that the safe harbor of salvation is open to persons of any religion whatever. They should consider the testimony of Christ Himself that ‘those who are not with Christ are against Him,’ (Lk 11:23), and that they disperse unhappily who do not gather with Him. Therefore ‘without a doubt, they will perish forever, unless they hold the Catholic faith whole and inviolate’ (Symbol. S. Athanasius). Let them hear Jerome who, while the Church was torn into three parts by schism, tells us that whenever someone tried to persuade him to join his group he always exclaimed: ‘He who is for the See of Peter is for me’ (St. Jerome, epistle 57). A schismatic flatters himself falsely if he asserts that he, too, has been washed in the waters of regeneration. Indeed Augustine would reply to such a man: ‘The branch has the same form when it has been cut off from the vine; but of what profit for it is the form, if it does not live from the root?’ (Gregory XVI. Encyclical Mirari vos, no. 13, August 15, 1832)

In particular, ensure that the faithful are deeply and thoroughly convinced of the truth of the doctrine that the Catholic faith is necessary for attaining salvation. The Catholic laity and clergy should repeatedly offer special thanks to God in public prayers for the priceless gift of the Catholic religion. They should also beseech God to protect the profession of this faith in our country and to keep it unharmed. (Pius IX. Encyclical Noscitis et nobiscum, December 8, 1849)

And here, beloved Sons and Venerable Brothers, We should mention again and censure a very grave error in which some Catholics are unhappily engaged, who believe that men living in error, and separated from the true faith and from Catholic unity, can attain eternal life. Indeed, this is certainly quite contrary to Catholic teaching. (Denzinger-Hünermann 2865-2867. Pius IX, Encyclical Quanto conficiamur moerore, August 10, 1863)

It is known to Us and to you that they who labor in invincible ignorance of our most holy religion and who, zealously keeping the natural law and its precepts engraved in the hearts of all by God, and being ready to obey God, live an honest and upright life, can, by the operating power of divine light and grace, attain eternal life, since God who clearly beholds, searches, and knows the minds, souls, thoughts, and habits of all men, because of His great goodness and mercy, will by no means suffer anyone to be punished with eternal torment who has not the guilt of deliberate sin.
But, the Catholic dogma that no one can be saved outside the Catholic Church is well-known; and also that those who are obstinate toward the authority and definitions of the same Church, and who persistently separate themselves from the unity of the Church, and from the Roman Pontiff, the successor of Peter, to whom ‘the guardianship of the vine has been entrusted by the Savior’, cannot obtain eternal salvation. (Denzinger-Hünermann 2865-2867. Pius IX, Encyclical Quanto conficiamur moerore, August 10, 1863)

[Condemned error:] Every man is free to embrace and profess that religion which he, led by the light of reason, thinks to be the true religion. In the worship of any religion whatever, men can find the way to eternal salvation, and can attain eternal salvation.
[Condemned error:] We must have at least good hope concerning the eternal salvation of all those who in no wise are in the true Church of Christ. (Denzinger-Hünermann 2915 – 2917. Pius IX, Syllabus of errors of our age – III Indifferentism, Latitudinarianism, 15-17)

As Our Apostolic duty, we wish your Episcopal solicitude and vigilance to be aroused, so that you will strive as much as you can to drive from the mind of men that impious and equally fatal opinion, namely, that the way of eternal salvation can be found in any religion whatsoever. May you demonstrate with that skill and learning in which you excel, to the people entrusted to your care that the dogmas of the Catholic faith are in no wise opposed to divine mercy and justice. (Pius IX, Allocution Singulari quadam, December 9, 1854)

We have committed to the protection and guidance of heaven those who do not belong to the visible Body of the Catholic Church […] ask each and every one of them to correspond to the interior movements of grace, and to seek to withdraw from that state in which they cannot be sure of their salvation. For even though by an unconscious desire and longing they have a certain relationship with the Mystical Body of the Redeemer, they still remain deprived of those many heavenly gifts and helps which can only be enjoyed in the Catholic Church. (Pius XII. Encyclical Mystici Corporis Christi, June 29, 1943)

This Sacred Council wishes to turn its attention firstly to the Catholic faithful. Basing itself upon Sacred Scripture and Tradition, it teaches that the Church, now sojourning on earth as an exile, is necessary for salvation. Christ, present to us in His Body, which is the Church, is the one Mediator and the unique way of salvation. In explicit terms He Himself affirmed the necessity of faith and baptism (cf. Mk. 16:16; Jn. 3:5) and thereby affirmed also the necessity of the Church, for through baptism as through a door men enter the Church. Whosoever, therefore, knowing that the Catholic Church was made necessary by Christ, would refuse to enter or to remain in it, could not be saved. (Vatican Council II. Dogmatic Constitution Lumen gentium, no. 14, November 21, 1964)

Since however we know not the day nor the hour, on Our Lord’s advice we must be constantly vigilant so that, having finished the course of our earthly life (cf. Heb 9:27), we may merit to enter into the marriage feast with Him and to be numbered among the blessed (Cf. Mt 25:31-46) and that we may not be ordered to go into eternal fire (Mt 25:41) like the wicked and slothful servant, (Cf. Mt 25:26) into the exterior darkness where ‘there will be the weeping and the gnashing of teeth’. (Mt 22:13 and 25:30) (Vatican Council II. Dogmatic Constitution Lumen gentium, no. 48, November 21, 1964)

God is the infinitely good and merciful Father. But man, called to respond to him freely, can unfortunately choose to reject his love and forgiveness once and for all, thus separating himself for ever from joyful communion with him. It is precisely this tragic situation that Christian doctrine explains when it speaks of eternal damnation or Hell.  (John Paul II. General Audience, July 28, 1999)

The problem of Hell has always disturbed great thinkers in the Church […] In point of fact, the ancient councils rejected the theory of the ‘final apocatastasis,’ according to which the world would be regenerated after destruction, and every creature would be saved; a theory which indirectly abolished hell. But the problem remains. Can God, who has loved man so much, permit the man who rejects Him to be condemned to eternal torment? And yet, the words of Christ are unequivocal. In Matthew’s Gospel He speaks clearly of those who will go to eternal punishment (cf. Mt 25:46). (John Paul II. Crossing the Threshold of Hope, pg. 96)

As the great Marxist Adorno said, only the resurrection of the body, which he claimed as unreal, would be able to create justice. We believe in this resurrection of the body in which not all will be equal. Today people have become used to thinking: what is sin? God is great, he knows us, so sin does not count; in the end God will be kind to us all. It is a beautiful hope. But both justice and true guilt exist. Those who have destroyed man and the earth cannot suddenly sit down at God’s table together with their victims. God creates justice. (Benedict XVI. Meeting with the Parish Priests and the Clergy of the Diocese of Rome, February 7, 2008)

We cannot be united with God unless we freely choose to love him. But we cannot love God if we sin gravely against him, against our neighbor or against ourselves: ‘He who does not love remains in death. Anyone who hates his brother is a murderer, and you know that no murderer has eternal life abiding in him’ (1Jn 3:14-15). Our Lord warns us that we shall be separated from him if we fail to meet the serious needs of the poor and the little ones who are his brethren (Mt 25:31- 46). To die in mortal sin without repenting and accepting God’s merciful love means remaining separated from him forever by our own free choice. (Catechism of the Catholic Church, no. 1033)