The Urim and Thummim By which the will of God was made known in doubtful cases, was put in this breast-plate, which is therefore called the breast-plate of judgment. Urim and Thummim signify light and integrity, or lights and perfections: many conjectures there are among the learned what they were: we have no reason to think they were any thing that Moses was to make, more than what was before ordered; so that either God made them himself, and gave them to Moses, for him to put into the breast-plate when other things were prepared; or, as is most probable, no more is meant but a declaration of the further use of what was already ordered to be made. The words may be read thus: And thou shalt give, or add, to the breast-plate of judgment, the illuminations and perfections, and they shall be upon the heart of Aaron That is, he shall be endued with a power of knowing and making known the mind of God in all difficult cases, relative either to the civil or ecclesiastical state. Their government was a theocracy; God was their king, the high-priest was, under God, their ruler, this Urim and Thummim were his cabinet council: probably Moses wrote upon the breast-plate, or wove into it, these words, Urim and Thummim, to signify that the high-priest, having on him this breast-plate, and asking counsel of God in any emergency, should be directed to those measures which God would own. If he were standing before the ark, probably he received instructions from off the mercy-seat, as Moses did, Exodus 25:22. If he were at a distance from the ark, as Abiathar was when he inquired of the Lord for David, (1 Samuel 23:6,) then the answer was given either by a voice from heaven, or by an impulse upon the mind of the high-priest, which last is perhaps intimated in that expression, He shall bear the judgment of the children of Israel upon his heart. This oracle was of great use to Israel. Joshua consulted it, (Numbers 27:21,) and it is likely, the judges after him. It was lost in the captivity, and never retrieved after. Indeed, according to the Jewish doctors, as Calmet observes, the custom of consulting God by Urim and Thummim continued no longer than under the tabernacle; for under the first temple, they say, (the temple of Solomon,) God spake by the prophets, and under the second temple, or after the captivity of Babylon, by bath koll, or the daughter of the voice, by which they mean a voice sent from heaven, as that which was heard at the baptism of Christ, at his transfiguration, and that mentioned John 12:28.
This Urim and Thummim, whatever they were, and in whatever way the will of God was made known by them, were no more than a shadow of good things to come, and the substance is Christ. He is our oracle; by him God in these last days makes known himself and his mind to us. Divine revelation centres in him, and comes to us through him; he is the light, the true light, the faithful witness; and from him we receive the Spirit of truth, who leads us into all truth. The joining of the breast-plate to the ephod signifies, that his prophetical office was founded on his priesthood; and it was by the merit of his death that he purchased this honour for himself, and this favour for us. It was the Lamb that had been slain that was worthy to take the book, and to open the seals, Revelation 5:9.