Exodus 28:39-40, 43

“Make the woven inner robe of fine linen, and make the turban of fine linen also. Make the cloth belt with designs sewn on it. Also make woven inner robes, cloth belts, and headbands for Aaron’s sons, to give them honor and beauty.

Aaron and his sons must wear these underclothes when they enter the Meeting Tent and anytime they come near the altar to serve as priests in the Holy Place. If they do not wear these clothes, they will be guilty of wrong, and they will die. This will be a law that will last from now on for Aaron and all his descendants.