Exodus 28:29-30

“In this way, Aaron will carry the names of the tribes of Israel on the sacred chestpiece over his heart when he goes into the Holy Place. This will be a continual reminder that he represents the people when he comes before the LORD. Insert the Urim and Thummim into the sacred chestpiece so they will be carried over Aaron’s heart when he goes into the LORD’s presence. In this way, Aaron will always carry over his heart the objects used to determine the LORD’s will for his people whenever he goes in before the LORD.