Virgins; by their father's and their own voluntary determination, as 1 Corinthians 7:37; neither is it said whether they continued in that state, but they were so. Which did prophesy; not by expounding the prophecies or word of God, for no woman is suffered to teach publicly, 1 Corinthians 14:34 1 Timothy 2:12; but rather foretelling things to come, which gift God did not debar that sex from; especially it having been promised, Joel 2:28, and in part fulfilled before, in Acts 2:17; by which God would show the enlargement of his mercies, and plenty of his Spirit, reserved for the times of the gospel.
Related Commentaries of Acts 21:9
Acts 21:9
9 And the same man had four daughters, virgins, which did prophesy.