Rashi on Leviticus 8:15/רש"י על ויקרא ח׳:ט״ו

1ויחטא את המזבח AND HE PURIFIED THE ALTAR — He cleansed and purified it from anything “strange” (alien to the sacred purpose for which the altar was intended) that may have happened to it, so that it might enter into a state of holiness (cf. Rashi on Exodus 19:36).

2ויקדשהו AND HE SANCTIFIED IT by this rite.

3לכפר עליו THAT ONE MIGHT MAKE EXPIATION UPON IT from that time onward with all atonement sacrifices (i. e. that all atonement sacrifices might henceforth be offered upon it; the meaning is not that he sanctified it so that he might now offer an atonement offering for it or upon it).