Exodus 28:30

28:30 “You are to put the Urim and the Thummim into the breastpiece of decision; and they are to be over Aaron’s heart when he goes in before the Lord. Aaron is to bear the decisions of the Israelites over his heart before the Lord continually.

Exodus 33:5

33:5 For the Lord had said to Moses, “Tell the Israelites, ‘You are a stiff-necked people. If I went up among you for a moment, I might destroy you. Now take off your ornaments, that I may know what I should do to you.’”