Love.
In my childhood, my pastor kept a picture of Jesus standing at the door and knocking in his office. Each year he would bring it out during a children's sermon and ask us what was wrong with the picture. The door had no handle. Every year he would remind us that we must open the door from the inside.
I've always wanted this same picture to hang in my office, but I don't like the tacky Americana version that is often for sale at garage sales - I wanted an icon of the scene. For years I have searched for an icon representing this verse in the Byzantine style to no avail. My friend's classmate is married to an icon painter, though ... so I finally decided that it was worth it to me to commission such an icon.
It's one of the most beautiful icons I've ever scene, and it has so much meaning to me - and it is something that will hang in my office for the rest of my life to remind me of God's great love and patience.