וּמָשַׁחְתָּ֣ אֹתָ֗ם כַּאֲשֶׁ֤ר מָשַׁ֙חְתָּ֙ אֶת־אֲבִיהֶ֔ם וְכִהֲנ֖וּ לִ֑י וְ֠הָיְתָה לִהְיֹ֨ת לָהֶ֧ם מָשְׁחָתָ֛ם לִכְהֻנַּ֥ת עוֹלָ֖ם לְדֹרֹתָֽם׃
And thou shalt anoint them, as thou didst anoint their father, that they may minister unto Me in the priest’s office; and their anointing shall be to them for an everlasting priesthood throughout their generations.’
Read kabbalistic (mystical) interpretation of Exodus 40:15: and classical mystical sources.