2 Corinthians 3:6

Not of the letter but of the spirit. Not of the law, but of grace. I am a minister of the New Testament, but not in such a way that I bring tables of the law and of the covenant and its words, as did Moses in the Old Testament, but so that God may by my words inspire into you heavenly thoughts and desires. Cf. Augustine. (de Spirit. et Lit. c. iii.).

For the letter killeth. (1.) Chrysostom, Ambrose, Augustine (de Doctr. Christ. lib. iii. c. 4) explain this to be that the letter of the law convicts and condemns them to death who do not obey this letter, i.e., the precepts of the law relating to righteousness and charity. For this letter of the law enacts that whosoever breaketh the law is to die the death. (2.) S. Augustine gives another explanation. If you abuse the literal meaning, and neglect the sense of Scripture, and fall into error, as Jews and heretics do, then the letter killeth. (3.) When metaphorical sayings are taken literally (S. Augustine, ibid. c. v., vi.). (4.) When types of the new law contained in the old are understood to be still binding in their literal meaning (ibid. Cf. also Origen, contra Celsum, lib. iii.; Didymus, de Spirit. Sanct. lib. iii.). The Fathers in general frequently say that the letter, i.e., the literal meaning of the law killeth, but the spirit, i.e., the spiritual and allegorical meaning, giveth life. This is because it is not now lawful to Christians to observe the ceremonies and ritual precepts of the old law literally under penalty of death; but they are bound to do what those ceremonies allegorically signified if they wish to attain the life of grace and glory. (5.) S. Augustine again in the same place says that the letter, both of the old and new law, killeth if separated from the spirit; but that this passage refers to the old law alone, because Moses, when he gave the law, gave only the letter, but Christ gave the spirit and the letter, and from this he lays down that the law cannot be fulfilled by the strength of nature alone, but requires the grace of Christ. (6.) S. Augustine once more and Anselm say that the letter killeth by giving occasion to sin; for the law is the occasion by which concupiscence is kindled and sin produced which kills the soul. This sense and the first are the most literal.

But the Spirit giveth life. (1.) The Spirit gives to the soul the supernatural life of grace and charity. (2.) He gives motives and strength for good works and for fulfilling the law. (3.) He guides us towards that eternal life promised by the law to them that keep it. Of this life and Spirit the Apostles were sent by Christ as ministers.