After making atonement for himself as well as the nation, the High Priest went to the altar for further expiatory and propitiatory work. The purification process reveals a degree of progression: it moves from the mercy seat to the tent to the altar in the courtyard.
18 Then he shall go out to the altar that is before the LORD and make atonement for it, and shall take some of the blood of the bull and some of the blood of the goat, and put it on the horns of the altar all around.