Adam Clarke on Exodus 28:12

Aaron shall bear their names before the Lord - He was to consider that he was the representative of the children of Israel; and the stones on the ephod and the stones on the breastplate were for a memorial to put Aaron in remembrance that he was the priest and mediator of the twelve tribes; and, speaking after the manner of men, God was to be put in mind of the children of Israel, their wants, etc., as frequently as the high priest appeared before him with the breastplate and the ephod. See Exo 28:29.