Rashi on Exodus 28:3/רש"י על שמות כ״ח:ג׳

1לקדשו לכהנו לי TO SANCTIFY HIM, TO APPOINT HIM AS PRIEST TO ME — to sanctify him, i. e. to instal him into the priesthood by means of the garments here specified, so that he may become priest unto Me. The expression of כהונה denotes service — serventrie in old French