Also put the Urim and the Thummim in the
breastpiece, so they may be over Aaron’s heart whenever he enters the presence
of the Lord.
Thus Aaron will always bear the means of making decisions for the Israelites
over his heart before the Lord. Exodus 28:30
The
Urim and Thummin were used to make decisions, sort of like casting lots,
throwing dice or flipping a coin. It
trusted God with the outcome, not considering it random, but divinely revealed. There isn’t a lot written about these tools,
so they’re very much a mystery.