The characteristic of a gate is that it swings back and forth but is never permanently shutting the observer out of viewing one side or another. Perhaps it is locked but we can see through it. A door, in contrast, shuts, and we cannot see what is on the other side. Hence the wisdom literature always speaks of the gate, seldom of the door — except, perhaps, to show how we do not know what is on the other side of some experiences. “Knock and it shall be opened” suggests that we are not sure what is on the other side of the door, that we do not know what to expect, that we are hoping for the best. Knocking on a door involves trepidation, anxiety, uncertainty. Like a child in a dark house, we need reassurance that what is behind the shut door is benign. Will the experience we are soliciting or pursuing (“knocking” on) be what we want or hope? Who can tell? This is called faith.