יחזקאל מג:כ פירוש: רש״י

on its four horns [i.e., the four horns] of the altar.

corners of the uppermost ledge the top of the altar.

and make it fit for atonement You shall “wipe” it of its ordinariness to initiate it into sanctity, so that it will befit for [providing] atonement from then on.