12:12-19 God's providence leaves room for the use of our prudence, though he has undertaken to perform and perfect what he has begun. These Christians continued in prayer for Peter, for they were truly in earnest. Thus men ought always to pray, and not to faint. As long as we are kept waiting for a mercy, we must continue praying for it. But sometimes that which we most earnestly wish for, we are most backward to believe. The Christian law of self-denial and of suffering for Christ, has not done away the natural law of caring for our own safety by lawful means. In times of public danger, all believers have God for their hiding-place; which is so secret, that the world cannot find them. Also, the instruments of persecution are themselves exposed to danger; the wrath of God hangs over all that engage in this hateful work. And the range of persecutors often vents itself on all in its way.

12-17. he came to the house of Mary, &c.—who "must have had a house of some pretensions to receive a large number; and, accordingly, we read that her brother Barnabas (Col 4:10) was a person of substance (Ac 4:37). She must also have been distinguished for faith and courage to allow such a meeting in the face of persecution" [Webster and Wilkinson]. To such a house it was natural that Peter should come.

mother of John … Mark—so called to distinguish him from the apostle of that name, and to distinguish her from the other Marys.

where many were gathered together praying—doubtless for Peter's deliverance, and continuing, no doubt, on this the last of the days of unleavened bread, which was their last hope, all night in prayer to God.