Hastings' Dictionary of the Bible (1898)
KNOCK, a summons to open the door, Jud 19:22; Cant. Song of Solomon 5:2; Acts 12:13; used as a sign of importunity. Matt 7:7-8; Luke 13:25, and of the signs of the coming of Christ. Luke 12:36; Rev 3:20. Oriental customs require knocking or calling at the outer door or gate, but not at the doors of rooms. Creditors were required by Moses to stand without and call. Deut 24:10-11.