The Angelic Doctor Against the Errors of the Greeks - Chapter 31

How the assertion that even the New Testament is a death-dealing letter is to be understood.

A further difficulty arises from a text of Athanasius in the letter to Serapion: “This is a deathdealing letter: From the beginning and before all ages I was created, etc. (Eccl. 24: 14),  and he adds many illustrations from the Old and New Testaments. The letter, however, of the New Testament does not seem to be deathdealing; for thus it would not differ from the letter of the Old Testament, about which 2 Cor. 3:6 says that the letter kills.

But a correct formulation should say that neither the letter of the New Testament nor that of the Old kills, except occasionally. Occasion of death some take in a twofold sense. In one sense, in so far as the sacred text is an occasion of error, something common both to the letter of the Old as well as the New Testament; hence St. Peter says in his second letter (3:16) that in the letters of St. Paul there are some things hard to understand, which the ignorant and unstable twist to their own destruction, as they do not understand the scriptures.

In another way, in so far as the precepts contained in Holy Scripture become the occasion for evil living, concupiscence being intensified by its prohibition when helping grace is not given; and in this way, the letter of the Old Testament is said to be death-dealing, but not the letter of the New.