פירוש על סוטה 15:11

And the priest grasps her clothing - in Makkot 22b, it's also taught "the attendant of the congregation takes hold of his clothes...". And it seems that because it is written about him "and he shall be degraded" (Deuteronomy 25:3), that it is a commandment to degrade him. In the Tosefta: "priests draw lots, and the one who draws the lot [to do this action], even the High Priest, goes and stands by the side of the sotah, and grasps her clothing"