וְחָגַרְתָּ֩ אֹתָ֨ם אַבְנֵ֜ט אַהֲרֹ֣ן וּבָנָ֗יו וְחָבַשְׁתָּ֤ לָהֶם֙ מִגְבָּעֹ֔ת וְהָיְתָ֥ה לָהֶ֛ם כְּהֻנָּ֖ה לְחֻקַּ֣ת עוֹלָ֑ם וּמִלֵּאתָ֥ יַֽד־אַהֲרֹ֖ן וְיַד־בָּנָֽיו׃
And thou shalt gird them with girdles, Aaron and his sons, and bind head-tires on them; and they shall have the priesthood by a perpetual statute; and thou shalt consecrate Aaron and his sons.
Read kabbalistic (mystical) interpretation of Exodus 29:9: and classical mystical sources.