A.T. Robertson Commentary Galatians 3:23

"But before faith came, we were kept in ward under the law, shut up unto the faith which should afterwards be revealed." — Galatians 3:23 (ASV)

Before faith came (προ του ελθειν την πιστιν). "Before the coming (second aorist active infinitive of ερχομα, definite event) as to the Faith" (note article, meaning the faith in verse 22 made possible by the historic coming of Christ the Redeemer), the faith in Christ as Saviour (verse 22).

We were kept in ward under the law (υπερ νομον εφρουρουμεθα). Imperfect passive of φρουρεω, to guard (from φρουρος, a guard). See on Ac 9:24; 2 Corinthians 11:32. It was a long progressive imprisonment.

Unto the faith which should afterwards be revealed (εις την μελλουσαν πιστιν αποκαλυφθηνα). "Unto the faith (verse 22 again) about to be revealed." Μελλω and the first aorist passive infinitive (regular idiom).