Revelation 3:20
20Behold, I stand at the door and knock: if any man hear my voice and open the door, I will come in to him, and will sup with him, and he with me.
Scripture Testimony Index stories for this passage
In conversation with Piotr about how he came to Christ, Richard Wurmbrand is surprised to learn that for Piotr, it was the stark contrast between Communism's forceful indoctrination and Jesus's subtle "knock at the door of our hearts".