A.T. Robertson Commentary Galatians 3:17

"Now this I say: A covenant confirmed beforehand by God, the law, which came four hundred and thirty years after, doth not disannul, so as to make the promise of none effect." — Galatians 3:17 (ASV)

Now this I say (τουτο δε λεγω). Now I mean this. He comes back to his main point and is not carried afield by the special application of σπερμα to Christ.

Confirmed beforehand by God (προκεκυρωμενην υπο του θεου). Perfect passive participle of προκυροω, in Byzantine writers and earliest use here. Nowhere else in N.T. The point is in προ and υπο του θεου (by God) and in μετα (after) as Burton shows.

Four hundred and thirty years after (μετα τετρακοσια κα τριακοντα ετη). Literally, "after four hundred and thirty years." This is the date in Ex 12:40 for the sojourn in Egypt (cf. Genesis 15:13). But the LXX adds words to include the time of the patriarchs in Canaan in this number of years which would cut the time in Egypt in two. Cf. Acts 7:6. It is immaterial to Paul's argument which chronology is adopted except that "the longer the covenant had been in force the more impressive is his statement" (Burton).

Doth not disannul (ουκ ακυρο). Late verb ακυροω, in N.T. only here and Mt 15:6; Mr 7:13 (from α privative and κυρος, authority). On καταργησα see 1 Corinthians 1:28; 2:6; 15:24,26.