"God can open doors. … He opens the doors of utterance and entrance for the Gospel. … He holds all the keys of every situation. He opens, and no man can shut. He shuts and no man can open. God, the Opener, is not on the outside, but on the inside of the barred doorway. "Knock and it shall be opened;" and the knock of faith surely implies waiting at the door with a purpose that remains unshaken, a faith that never wavers."
— Samuel M. Zwemer
Source: The Unoccupied Mission Fields of Africa and Asia (1911), pp. 90–91