וְהִקְרַבְתָּ֤ אֶֽת־אַהֲרֹן֙ וְאֶת־בָּנָ֔יו אֶל־פֶּ֖תַח אֹ֣הֶל מוֹעֵ֑ד וְרָחַצְתָּ֥ אֹתָ֖ם בַּמָּֽיִם׃
And thou shalt bring Aaron and his sons unto the door of the tent of meeting, and shalt wash them with water.
Read kabbalistic (mystical) interpretation of Exodus 40:12: and classical mystical sources.