"and he shall bring him near to the door or to the door-post": The door is being compared to the door-post, viz.: Just as a door-post stands in its place, so, the door must be standing in its place. And this would follow a fortiori, viz.: If the door, which is not kasher for the mitzvah (of mezuzah), is kasher for boring, then the door-post, which is kasher for the mitzvah of mezuzah, how much more so should it be kasher for boring!
It is, therefore, written (Devarim 15:17) "Then you shall take the awl and place it in his ear and in the door" — You place it in the door, but not in the door-post. But perhaps the awl is to pierce both his ear and the door-post; it is, therefore, written (Exodus 21:6) "then his master shall bore his ear with an awl" — his ear is pierced and not the door. It is the first reading, then, which is to be accepted — The door is being compared to the door-post, viz.: Just as a door-post stands in its place, so, the door must be standing in its place.