Lord, I had believed that I was something of myself, I judged myself to be self-sufficient, without realizing that You governed me, until you distanced yourself from me, and then I realized, and saw and recognized that it was You who had helped me; that if I fell it was my fault, and if I got up it was because of You. You have opened my eyes, divine light, and have lifted me up and illuminated me; and I have observed that the life of man on this earth is a test, and that no flesh can boast before you, nor is any living being justified, because all good, great or small, is Your gift, and ours is only evil. What then may flesh boast of? Evil, perhaps? But this is not glory but misery. Could one boast of some good, even though not one’s own? But all good is Yours, Lord, and Yours is the glory. (Saint Augustine of Hippo (attrib.). Soliloquies of the soul to God, 15)

Then he gives the reason for the Lord’s response when he says, ‘for my power is made perfect in weakness [infirmity]’. This is a remarkable expression: virtue is made perfect in infirmity… But this can be understood in two ways, namely, materially and by way of occasion. If it is taken materially, the sense is this: infirmity is the material on which to exercise virtue; first, humility, as stated above; secondly, patience: ‘The testing of your faith produces steadfastness’ (Jas 1:3); thirdly, temperance, because hunger is weakened by infirmity and a person is made temperate. But if it is taken as an occasion, infirmity is the occasion for arriving at perfect virtue, because a man who knows that he is weak is more careful when resisting, and as a result of fighting and resisting more he is better exercised and, therefore, stronger. (Saint Thomas Aquinas. Commentary of the Second Letter to the Corinthians, lect. 3: 2Cor 12:7-10 (no. 479))

Then the Apostle mentions the effect of this answer from the Lord, saying: I will all the more gladly boast of my weaknesses, that the power of Christ may rest upon me. He mentions two effects. One is glorying; hence he says: because my virtue is made perfect in infirmity, I will all the more gladly boast of my weaknesses, i.e., given to me for my profit; and this because it joins me closer to Christ: ‘But far be it from me to glory except in the cross of our Lord Jesus Christ’ (Gal 6:14); […] The reason I will glory gladly is that the power of Christ may rest upon me [dwell in me], i.e., that through infirmity the grace of Christ may dwell and be made perfect in me: ‘He gives power to the faint, and to him who has no might he increases strength’ (Is 40:29). The other effect is joy. Hence he says: For the sake of Christ, then, I am content with weaknesses. In regard to this he does two things. First, he mentions the effect of joy; secondly, he assigns the reason for it (v. 10b). (Saint Thomas Aquinas. Commentary of the Second Letter to the Corinthians, lect. 3: 2 Cor. 12:7-10 (no. 480-481))

The other effect is joy. Hence he says: For the sake of Christ, then, I am content with weaknesses. In regard to this he does two things. First, he mentions the effect of joy; secondly, he assigns the reason for it. He mentions the effect of joy and the matter of joy. He says therefore: ‘Because the power of Christ dwells in me in all tribulations, I am content’, i.e., I am greatly pleased and take joy in the infirmities I mentioned: ‘Count it all joy, my brethren, when you meet various trials’ (Jas. 1:2). […] But in all these things the material which makes for joy is that they are for Christ. As if to say: I am pleased because I suffer for Christ: ‘But let none of you suffer as a murderer, or a thief’ (1 Pet 4:15). […] He assigns the reason for this joy, when he says, ‘for when I am weak, then I am strong,’ i.e., when as a result of what is in me or as a result of persecutions, I fall into any of the aforesaid, God’s help is applied to me to strengthen me. (Saint Thomas Aquinas. Commentary of the Second Letter to the Corinthians, lect.3: 2 Cor. 12:7-10 (no. 480-481))

He [St. Paul] recognized that he is nothing on his own; and that all that he is must be attributed to the grace of God, not to his own strength. He recognized what is written, I will glory of my infirmities; recognized the truth of the words, To the humble He gives his grace, and he has been weakened; you however have strengthened him because power is made perfect in weakness. (Saint Augustine of Hippo. Exposition on Psalm 67, no. 12)

Power is perfected in weakness, for weakness obliges us to combat. The greater the facility in victory, the lesser is the effort in combat. How can one fight against himself, if he finds no resistance in his interior? And, what is that which resists within us if not that which needs to be cured, to be healed? Weakness is then, the only cause that obliges us to initiate a combat within ourselves; and weakness itself is a warning for us not to become proud. Consequently, the power that holds our pride in check when we may feel arrogant, is perfected in weakness. (Saint Augustine of Hippo. Reply to Julian, Book IV, 11 – Italian)

Here he hints at another thing also, namely, that in proportion as the trials waxed in intensity, in the same proportion the grace was increased and continued.

‘Wherefore I take pleasure in many weaknesses’ (2Cor 12:10). Of what sort? Tell me. ‘In injuries, in persecutions, in necessities, in distresses.’ Do you see how he has now revealed it in the clearest manner? For in mentioning the species of the infirmity he spoke not of fevers, nor any return of that sort, nor any other bodily ailment, but of ‘injuries, persecutions, distresses.’ Do you see a single-minded soul? He longs to be delivered from those dangers; but when he heard God’s answer that this befits not, he was not only not sorry that he was disappointed of his prayer, but was even glad. Wherefore he said, ‘I take pleasure,’ ‘I rejoice, I long, to be injured, persecuted, distressed for Christ’s sake.’ And he said these things both to check those, and to raise the spirits of these that they might not be ashamed at Paul’s sufferings. […] ‘For when I am weak, then am I strong.’ Why do you marvel that the power of God is then conspicuous? I too am strong ‘then’; for then most of all did grace come upon him. ‘For as His sufferings abound, so does our consolation abound also.’ Where affliction is, there is also consolation; where consolation, there is grace also. (Saint John Chrysostom. Homily on Second Corinthians, Homily 26, no. 3)

Do you see that he nowhere glories of miracles, but of his persecutions and his trials? For this is meant by ‘weaknesses.’ (Saint John Chrysostom. Homily on Second Corinthians, Homily 25, no. 2)

Gladly, says the Apostle, will I glory in my infirmities, that the power of Christ may dwell in me (2Cor 12:9). We, too, should say the same: we should glory in the knowledge of our insufficiency, that thus we may acquire the power of Jesus Christ, that is, holy humility. (Saint Alphonsus de Liguori. Selva of material for preaching , part II, ch. 6, no.3)

What are the weaknesses that the Apostle is talking about? […] his attitude enables us to realize that every difficulty in following Christ and witnessing to his Gospel may be overcome by opening oneself with trust to the Lord’s action. St Paul is well aware that he is an ‘unworthy servant’ (Lk 17:10) — it is not he who has done great things, it is the Lord — an ‘earthen vessel’ (2Cor 4:7), in which God places the riches and power of his Grace. (Benedict XVI. General audience, June 13, 2012)

In this moment of concentrated contemplative prayer, St Paul understands clearly how to face and how to live every event, especially suffering, difficulty and persecution. The power of God, who does not abandon us or leave us on our own but becomes our support and strength, is revealed at the very moment when we experience our own weakness. (Benedict XVI. General audience, June 13, 2012)

The Lord does not free us from evils, but helps us to mature in sufferings, difficulties and persecutions. […] Therefore, to the extent that our union with the Lord increases and that our prayers become intense, we also go to the essential and understand that it is not the power of our own means, our virtues, our skills that brings about the Kingdom of God but that it is God who works miracles precisely through our weakness, our inadequacy for the task. We must therefore have the humility not to trust merely in ourselves, but to work, with the Lord’s help, in the Lord’s vineyard, entrusting ourselves to him as fragile ‘earthen vessels’.(Benedict XVI. General audience, June 13, 2012)

The way of perfection passes by way of the Cross. There is no holiness without renunciation and spiritual battle. Spiritual progress entails the ascesis and mortification that gradually lead to living in the peace and joy of the Beatitudes. (Catechism of the Catholic Church, no. 2015)

God shows forth his almighty power by converting us from our sins and restoring us to his friendship by grace. ‘God, you show your almighty power above all in your mercy and forgiveness. . .’ (Roman Missal, 26th Sunday, Opening Prayer). (Catechism of the Catholic Church, no. 277)

The Apostle Paul has, moreover, in the most lucid manner, pointed out that man has been delivered over to his own infirmity, lest, being uplifted, he might fall away from the truth. […] My grace is sufficient for thee; for strength is made perfect in weakness. Gladly therefore shall I rather glory in infirmities, that the power of Christ may dwell in me. What, therefore? (as some may exclaim) did the Lord wish, in that case, that His apostles should thus undergo buffering, and that he should endure such infirmity? Even so it was; the word says it. For strength is made perfect in weakness, rendering him a better man who by means of his infirmity becomes acquainted with the power of God. For how could a man have learned that he is himself an infirm being, and mortal by nature, but that God is immortal and powerful, unless he had learned by experience what is in both? (Saint Irenaeus. Against Heresies. Bk.5, ch. III, 503)

Sin is thus ‘love of oneself even to contempt of God.’ (St. Augustine, De civ. Dei 14, 28) In this proud self-exaltation, sin is diametrically opposed to the obedience of Jesus, which achieves our salvation (cf. Phil 2:6-9). (Catechism of the Catholic Church, no. 1850)

Sin sets itself against God’s love for us and turns our hearts away from it. (Catechism of the Catholic Church, no. 1850)

If you do not take into account your sin, considering it light, at least be afraid of the gravity of the chastisement. But you would insist: ‘they are little things, trifling details, which live here below cannot be exempt from. Very well, gather together all these trifles and you will see if they do not form an enormous mass. Like the grains of wheat: so small, and yet they form a great heap; or like the drops of water, which although so small, form rivers and drag away even the boulders. The psalmist meditates on the innumerable sins, small ones perchance, that man commits every day, considering only those in thought and with the tongue, yet it does not escape him that putting together many light sins a great heap is made. (Saint Augustine of Hippo. Expositions on Psalm 129, no. 5)

Let a man but have his soul’s sense of smelling sound, he perceives how foully sins stink. (Saint Augustine of Hippo. Expositions on Psalm 38 (37), 8)

And this is the definition of sin: a deviated use, and contrary to the will God, of the faculties that God has given us to practice good; just as, virtue, on the contrary, which God seeks [of us], consists in using these faculties with an upright conscience, proceeding in accordance with the Lord’s command. (Saint Basil the Great. Greater Monastic Rule, resp. 2, 1: PG 31, 910)

‘Sin is an abuse of the freedom that God gives to created persons so that they are capable of loving him and loving one another’ (Catechism, 387); it is refusal to live the life of God received in Baptism, to let ourselves be loved by the true Love: the human being has in fact the terrible power to be an obstacle to God who wills to give all that is good. Sin, which has its origin in the person’s free will (Mk 7:20), is failure in genuine love; it wounds the nature of the human person and injures human solidarity by attitudes, words and actions steeped in self-love (cf. Catechism, 1849-1850). (John Paul II. Message on the occasion of the 14th World Youth Day, January 9, 1999)

The Church, taking her inspiration from Revelation, believes and professes that sin is an offense against God. (John Paul II. Encyclical Dominum et vivificantem, no. 39, May 18, 1986)

For man also knows, through painful experience, that by a conscious and free act of his will he can change course and go in a direction opposed to God’s will, separating himself from God (aversio a Deo), rejecting loving communion with him, detaching himself from the life principle which God is and consequently choosing death. (John Paul II. Apostolic exhortation Reconciliatio et paenitentia, no. 17, December 2, 1984)

With the whole tradition of the church, we call mortal sin the act by which man freely and consciously rejects God, his law, the covenant of love that God offers, preferring to turn in on himself or to some created and finite reality, something contrary to the divine will (conversio ad creaturam). (John Paul II. Apostolic Exhortation Reconciliatio et paenitentia, no. 17, December 2, 1984)

Man perceives that this disobedience to God destroys the bond that unites him with his life principle: It is a mortal sin, that is, an act which gravely offends God and ends in turning against man himself with a dark and powerful force of destruction. (John Paul II. Apostolic exhortation Reconciliatio et paenitentia, no. 17)

Sin is the distortion or destruction of the relationship with God, this is its essence: it ruins the relationship with God, the fundamental relationship, by putting ourselves in God’s place. (Benedict XVI. General audience, February 6, 2013)

‘Begin to the Lord in confession’ (Ps146:7). Begin with this, if you would arrive at a clear understanding of the truth. If you will be brought from the road of faith to the profession of the reality, ‘begin in confession’. First accuse yourself: accuse yourself, praise God. What after confession? Let good works follow. ‘Sing unto our God upon the harp’. What is, ‘upon the harp’? As I have already explained, just like the Psalm upon the psaltery, so also is the ‘harp’: not with voice only, but with works. (Saint Augustine of Hippo. Expositions on Psalm 148, 11)

‘God created us without us: but he did not will to save us without us’ (St. Augustine, Sermon 169, 11-13). To receive his mercy, we must admit our faults. ‘If we say we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, he is faithful and just, and will forgive our sins and cleanse us from all unrighteousness’ (Jn 8-9). As Saint Paul affirms, ‘Where sin increased, grace abounded all the more’ (Rom 5:20). But to do its work grace must uncover sin so as to convert our hearts and bestow on us ‘righteousness to eternal life through Jesus Christ our Lord’ (Rom 5:21). (Catechism of the Catholic Church, no. 1847-1848)

For not so much sinning, as sinning without even pain, causes in Him indignation and wrath. Wherefore it were meet after all this to sink into the very earth, and not so much as to behold this sun, nor to breathe at all, for that having so placable a Master, we provoke Him first, and then have no remorse for provoking Him. (Saint John Chrysostom. Homily 14 on Saint Matthew, no. 5)

The best thing then is, to avoid sin in the first instance: the next to it, is to feel that we sin, and thoroughly amend ourselves. But if we have not this, how shall we pray to God, and ask forgiveness of our sins, we who take no account of these matters? For when you yourself who hast offended art unwilling to know so much as this very fact, that you have sinned; for what manner of offenses will you entreat God for pardon? (Saint John Chrysostom. Homily 14 on Saint Matthew, no. 5)

And so the soul which has ever so little consented to sin, ought to abhor itself and make haste to seek purification, out of respect to His Divine Gaze Who beholds it always. Why should we die a spiritual death when there is a sovereign remedy available? (Saint Francis de Sales. Introduction to the Devout Life, ch. XIX)

As it is known, the Father that has made us his children through Baptism, remains faithful to his love even when, by his own fault, man separates from Him. His mercy is stronger than sin, and the Sacrament of Confession is its most expressive sign, like a second Baptism, as the Fathers of the Church call it. Effectively, in Confession the same grace of Baptism is renewed precisely by a newer and richer insertion into the mystery of Christ and the Church. (John Paul II. Address to the clergy of Todi and Orvieto, November 22, 1981)