A.T. Robertson Commentary Galatians 3:8

"And the scripture, foreseeing that God would justify the Gentiles by faith, preached the gospel beforehand unto Abraham, [saying,] In thee shall all the nations be blessed." — Galatians 3:8 (ASV)

Foreseeing (προιδουσα). Second aorist active participle of προοραω. The Scripture is here personified. Alone in this sense of "sight," but common with λεγε or ειπεν (says, said) and really in verse 22 "hath shut up" (συνεκλεισεν).

Would justify (δικαιο). Present active indicative, "does justify."

Preached the gospel beforehand (προευηγγελισατο). First aorist middle indicative of προευαγγελιζομα with augment on α though both προ and ευ before it in composition. Only instance in N.T. It occurs in Philo. and Schol. Soph. This Scripture announced beforehand the gospel on this point of justification by faith. He quotes the promise to Abraham in Ge 12:3; 18:18, putting παντα τα εθνη (all the nations) in 18:18 for πασα α φυλα (all the tribes) of the earth. It is a crucial passage for Paul's point, showing that the promise to Abraham included all the nations of the earth. The verb ενευλογεω (future passive here) occurs in the LXX and here only in N.T. (not Ac 3:25 in correct text).

In thee (εν σο). "As their spiritual progenitor" (Lightfoot).