Before faith came (pro tou elthein tēn pistin). “Before the coming (second aorist active infinitive of erchomai, definite event) as to the Faith” (note article, meaning the faith in Gal 3:22 made possible by the historic coming of Christ the Redeemer), the faith in Christ as Saviour (Gal 3:22).
We were kept in ward under the law (huper nomon ephrouroumetha). Imperfect passive of phroureō, to guard (from phrouros, a guard). See note on Act 9:24; note on 2Co 11:32. It was a long progressive imprisonment.
Unto the faith which should afterwards be revealed (eis tēn mellousan pistin apokaluphthēnai). “Unto the faith (Gal 3:22 again) about to be revealed.” Mellō and the first aorist passive infinitive (regular idiom).