Revelation 7:9 behold I stand at the door and knock... 

On the stone doorstep are carved my initials, the only indication that this is my painting, my home. Living in Africa I found that many doors do not have door knobs. The only way in is if someone on the inside recognizes the voice of the visitor and opens the door from the inside. Our souls are the same. When Jesus says he is standing at the door of my soul and knocking the only way in for him is if I open the door.