2 Corinthians 3:5-6
“Not that we are sufficient of ourselves to account any thing as from ourselves.”
See again, yet another corrective. For he possesses this virtue, humility I mean, in singular perfection. Wherefore whenever he says any thing great of himself, he makes all diligence to soften down extremely and by every means, what he has said. And so he does in this place also, saying, “Not that we are sufficient of ourselves to account any thing as from ourselves:” that is, I said not, “We have confidence,” as though part were ours and part God's; but I refer and ascribe the whole to Him.
“For our sufficiency is from God; who also made us sufficient as ministers of a new covenant.”
What means, “made us sufficient?” Made us able and fitting. And it is not a little thing to be the bearer to the world of such tables and letters, greater far than the former. Whence also he added,
“Not of the letter, but of the spirit.” See again another difference. What then? Was not that Law spiritual? How then says he, “We know that the Law is spiritual?” Spiritual indeed, but it bestowed not a spirit. For Moses bare not a spirit, but letters; but we have been entrusted with the giving of a spirit. Whence also in further completion of this [contrast,] he says,
“For the letter kills, but the spirit gives life.”
Yet these things he says not absolutely; but in allusion to those who prided themselves upon the things of Judaism. And by “letter” here he means the Law which punishes them that transgress; but by “spirit” the grace which through Baptism gives life to them who by sins were made dead. For having mentioned the difference arising from the nature of the tables, he does not dwell upon it, but rapidly passing it by, bestows more labor upon this, which most enabled him to lay hold on his hearer from considerations of what was advantageous and easy; for, says he, it is not laborious, and the gift it offers is greater. For if when discoursing of Christ, he puts especially forward those things which are of His lovingkindness, more than of our merit, and which are mutually connected, much greater necessity is there for his doing so when treating of the covenant. What then is the meaning of “the letter kills?” He had said tables of stone and hearts of flesh: so far he seemed to mention no great difference. He added that the former [covenant] was written with letters or ink, but this with the Spirit. Neither did this rouse them thoroughly, He says at last what is indeed enough to give them wings; the one “kills,” the other “gives life.” And what does this mean? In the Law, he that has sin is punished; here, he that has sins comes and is baptized and is made righteous, and being made righteous, he lives, being delivered from the death of sin. The Law, if it lay hold on a murderer, puts him to death; the Gospel, if it lay hold on a murderer, enlightens, and gives him life. And why do I instance a murderer? The Law laid hold on one that gathered sticks on a sabbath day, and stoned him. This is the meaning of, “the letter kills.” The Gospel takes hold on thousands of homicides and robbers, and baptizing delivers them from their former vices. This is the meaning of, “the Spirit gives life.” The former makes its captive dead from being alive, the latter renders the man it has convicted alive from being dead. For, “come unto me, you that labor and are heavy laden,” and, He said not, 'I will punish you,' but, “I will give you rest.” For in Baptism the sins are buried, the former things are blotted out, the man is made alive, the entire grace written upon his heart as it were a table. Consider then how high is the dignity of the Spirit, seeing that His tables are better than those former ones; seeing that even a greater thing is shown forth than the resurrection itself. For indeed, that state of death from which He delivers, is more irremediable than the former one: as much more so, as soul is of more value than the body: and this life is conferred by that, by that which the Spirit gives. But if It be able to bestow this, much more then that which is less. For, that prophets wrought, but this they could not: for none can remit sins but God only; nor did the prophets bestow that life without the Spirit. But this is not the marvel only, that it gives life, but that it enabled others also to do this. For He says, “Receive the Holy Ghost.” Wherefore? Because without the Spirit it might not be? [Yes,] but God, as showing that It is of supreme authority, and of that Kingly Essence, and has the same power [with Himself,] says this too. Whence also He adds, “Whosesoever sins ye remit, they are remitted; and whosesoever sins ye retain, they are retained.”
Source: Homilies on Second Corinthians (New Advent)