Urim and Thummim

Boyd’s Bible Dictionary:

(light and perfection). From the way these mysterious words are spoken of (Ex. 28:3030And thou shalt put in the breastplate of judgment the Urim and the Thummim; and they shall be upon Aaron's heart, when he goeth in before the Lord: and Aaron shall bear the judgment of the children of Israel upon his heart before the Lord continually. (Exodus 28:30)), and (Lev. 8:88And he put the breastplate upon him: also he put in the breastplate the Urim and the Thummim. (Leviticus 8:8)), compared with (Ex. 28:15-2115And thou shalt make the breastplate of judgment with cunning work; after the work of the ephod thou shalt make it; of gold, of blue, and of purple, and of scarlet, and of fine twined linen, shalt thou make it. 16Foursquare it shall be being doubled; a span shall be the length thereof, and a span shall be the breadth thereof. 17And thou shalt set in it settings of stones, even four rows of stones: the first row shall be a sardius, a topaz, and a carbuncle: this shall be the first row. 18And the second row shall be an emerald, a sapphire, and a diamond. 19And the third row a ligure, an agate, and an amethyst. 20And the fourth row a beryl, and an onyx, and a jasper: they shall be set in gold in their inclosings. 21And the stones shall be with the names of the children of Israel, twelve, according to their names, like the engravings of a signet; every one with his name shall they be according to the twelve tribes. (Exodus 28:15‑21)), they appear to denote some material things, separate from the high priest’s breastplate and its gems, and previously well known. Their purpose seems to be indicated (Num. 27:2121And he shall stand before Eleazar the priest, who shall ask counsel for him after the judgment of Urim before the Lord: at his word shall they go out, and at his word they shall come in, both he, and all the children of Israel with him, even all the congregation. (Numbers 27:21); 1 Sam. 28:66And when Saul inquired of the Lord, the Lord answered him not, neither by dreams, nor by Urim, nor by prophets. (1 Samuel 28:6)), and, since they were connected with the ephod (1 Sam. 22:14-15; 23:9-12; 30:7-814Then Ahimelech answered the king, and said, And who is so faithful among all thy servants as David, which is the king's son in law, and goeth at thy bidding, and is honorable in thine house? 15Did I then begin to inquire of God for him? be it far from me: let not the king impute any thing unto his servant, nor to all the house of my father: for thy servant knew nothing of all this, less or more. (1 Samuel 22:14‑15)
9And David knew that Saul secretly practised mischief against him; and he said to Abiathar the priest, Bring hither the ephod. 10Then said David, O Lord God of Israel, thy servant hath certainly heard that Saul seeketh to come to Keilah, to destroy the city for my sake. 11Will the men of Keilah deliver me up into his hand? will Saul come down, as thy servant hath heard? O Lord God of Israel, I beseech thee, tell thy servant. And the Lord said, He will come down. 12Then said David, Will the men of Keilah deliver me and my men into the hand of Saul? And the Lord said, They will deliver thee up. (1 Samuel 23:9‑12)
7And David said to Abiathar the priest, Ahimelech's son, I pray thee, bring me hither the ephod. And Abiathar brought thither the ephod to David. 8And David inquired at the Lord, saying, Shall I pursue after this troop? shall I overtake them? And he answered him, Pursue: for thou shalt surely overtake them, and without fail recover all. (1 Samuel 30:7‑8)), it may be inferred they were consulted to ascertain the will of Jehovah, and that they were preserved in the bag of the high priest’s breastplate to be borne “upon his heart before the Lord continually” (Ex. 28:3030And thou shalt put in the breastplate of judgment the Urim and the Thummim; and they shall be upon Aaron's heart, when he goeth in before the Lord: and Aaron shall bear the judgment of the children of Israel upon his heart before the Lord continually. (Exodus 28:30)). Not in use after the captivity (Ezra 2:6363And the Tirshatha said unto them, that they should not eat of the most holy things, till there stood up a priest with Urim and with Thummim. (Ezra 2:63); Neh. 7:6565And the Tirshatha said unto them, that they should not eat of the most holy things, till there stood up a priest with Urim and Thummim. (Nehemiah 7:65); Hos. 3:44For the children of Israel shall abide many days without a king, and without a prince, and without a sacrifice, and without an image, and without an ephod, and without teraphim: (Hosea 3:4)).

Concise Bible Dictionary:

The signification of these Hebrew words is “lights” and “perfections.” They were distinct from the gems on the breastplate, for Moses put the breastplate upon Aaron, “also he put in [or ‘on’] the breastplate the Urim and the Thummim” (Lev. 8:88And he put the breastplate upon him: also he put in the breastplate the Urim and the Thummim. (Leviticus 8:8)). It is clear that God answered questions by means of the Urim and Thummim (Num. 27:2121And he shall stand before Eleazar the priest, who shall ask counsel for him after the judgment of Urim before the Lord: at his word shall they go out, and at his word they shall come in, both he, and all the children of Israel with him, even all the congregation. (Numbers 27:21); Deut. 33:88And of Levi he said, Let thy Thummim and thy Urim be with thy holy one, whom thou didst prove at Massah, and with whom thou didst strive at the waters of Meribah; (Deuteronomy 33:8); 1 Sam. 28:66And when Saul inquired of the Lord, the Lord answered him not, neither by dreams, nor by Urim, nor by prophets. (1 Samuel 28:6)). On the return of the Jews from Babylon some, who claimed to be priests but could not show their genealogy, were not allowed to eat of the holy things until there should stand up a priest with Urim and Thummim, and an answer be obtained from God. This great privilege has never yet been restored (Ezra 2:6363And the Tirshatha said unto them, that they should not eat of the most holy things, till there stood up a priest with Urim and with Thummim. (Ezra 2:63); Neh. 7:6565And the Tirshatha said unto them, that they should not eat of the most holy things, till there stood up a priest with Urim and Thummim. (Nehemiah 7:65)).
It may be remarked that there is no record as to the construction of the Urim and Thummim, nor of their form. The first mention of them is in Exodus 28:3030And thou shalt put in the breastplate of judgment the Urim and the Thummim; and they shall be upon Aaron's heart, when he goeth in before the Lord: and Aaron shall bear the judgment of the children of Israel upon his heart before the Lord continually. (Exodus 28:30): “Thou shalt put in [or ‘on’] the breastplate of judgment the Urim and the Thummim; and they shall be upon Aaron's heart when he goeth in before the Lord,” as if God had given them to Moses, and had merely to tell him what to do with them—if indeed they were material things; but what they were, and how the answers were given, is not revealed. When Israel is restored, Christ Himself will take the place of the ancient Urim and Thummim.