“lex per Mosen data est,” John writes, “gratia et veritas per Iesum Christum facta est” (Jn 1:17). These are strong words, words — on their face — to warm a Marcionite’s heart. The Law, given through Moses, apparently excludes “grace and truth,” which come through Jesus. What to make of this? Augustine seeks to minimize the force of this verse, by reading it through the more extensive, but parallel discussion of the Law in Romans. “Per servum Lex data est; reos fecit,” Augustine notes, while, “per Imperatorem indulgentia data est; reos liberavit” (Tractatus in Iohannis Evangelium 3.16). Just as for Paul, the commandment of the Law goads the sinner to his sin, and so makes sin “exceedingly sinful” (Rom 7:13, cf. 7:7-13), so too for John, the Law does not give what it commands, and so it remains for “grace” to come through Christ. This reading has some traction elsewhere in the Gospel; something like Paul’s reflection on Israel’s failure to abide by the Law might be presupposed by John 7:19: “Did not Moses give you the law, and yet none of you keepeth the law?”
Aquinas, however, takes a more dialectical approach, one that preserves a more positive role for the Law. He begins his comparison of Moses and Christ with John’s teaching, “De plenitudine eius nos omnes accepimus et gratiam pro gratia” (Jn 1:16). He interprets “gratiam pro gratia” as “de plenitudine eius accepimus gratiam, et pro illa gratia accepimus aliam” (i.e., the grace given by Christ supersedes a “first grace”) (Commentary on John, Cap. 1, Lec. 10). He agrees with Chrysostom that this first grace “fuit gratia veteris testamenti accepta in lege, quae quidem magna fuit, iuxta illud Prov. IV, v. 2: donum bonum tribuam vobis et cetera. Magnum enim fuit quod hominibus idolatris data sunt praecepta a Deo, et unius veri Dei vera cognitio” (Ibid.). He turns to another part of Romans to illuminate this thesis: “Rom. III, 1: quid amplius Iudaeo, aut quae utilitas circumcisionis? Multum quidem per omnem modum. Primum quidem quia credita sunt eis eloquia Dei” (Ibid., cf. Rom 9:4-5). And here again, this thesis finds plenty to illuminate it elsewhere in John, not least in Jesus’ insistence that Moses “wrote about me” (Jn 5:46).
Only after affirming the goodness of the Law — and rooting that affirmation squarely in John 1 itself! — does Aquinas take up the negative thesis that Augustine highlights: “Sed numquid non sufficiebat prima gratia? Respondeo dicendum, quod non, quia per legem solum cognitio peccati datur, non ablatio. Neminem enim ad perfectum adduxit lex, Hebr. VII, 19. Et ideo erat necesse quod alia gratia peccata auferens, et reconcilians Deo, veniret” (Commentary on John, Cap. 1, Lec. 10).