“Urim and Thummim” means light and perfection
Urim and Thummim: When the Jewish exiles were met on their return from Babylon by a question which they had no data for answering, they agreed to postpone the settlement of the difficulty till there should rise up "a priest with Urim and Thummim." (Ezra 2:63; Nehemiah 7:65) The inquiry what those Urim and Thummim themselves were seems likely to wait as long for a final and satisfying answer. On every side we meet with confessions of ignorance. Urim means "light," and Thummim "perfection." Scriptural statements. --The mysterious words meet us for the first time, as if they needed no explanation, in the description of the high Priest's apparel. Over the ephod there is to be a "breastplate of judgment" of gold, scarlet, purple and fine linen, folded square and doubled, a "span" in length and width. In it are to be set four rows of precious stones, each stone with the name of a tribe of Israel engraved on it, that Aaron "may bear them on his heart." Then comes a further order. In side the breastplate, as the tables of the covenant were placed inside the ark, (Exodus 25:16; 28:30) are to be placed "the Urim and the Thummim," the light and the perfection; and they too are to be on Aaron's heart when he goes in before the Lord. (Exodus 28:15-30) Not a word describes them. They are mentioned as things-already familiar both to Moses and the people, connected naturally with the functions of the high priest as mediating between Jehovah and his people. The command is fulfilled. (Leviticus 8:8) They pass from Aaron to Eleazar with the sacred ephod and other pontificalia . (Numbers 20:28) When Joshua is solemnly appointed to succeed the great hero-law-giver he is bidden to stand before Eleazar, the priest, "who shall ask counsel for him after the judgment of Urim," and this counsel is to determine the movements of the host of Israel. (Numbers 27:21) In the blessings of Moses they appear as the crowning glory of the tribe of Levi: "thy Thummim and thy Urim are with thy Holy One." (33:8,9) In what way the Urim and Thummim were consulted is quite uncertain. Josephus and the rabbins supposed that the stones gave out the oracular answer by preternatural illumination; but it seems to be far simpler and more in agreement with the different accounts of inquiries made by Urim and Thummim, (1 Samuel 14:3,18,19; 23:2,4,9,11,12; 28:6; Judges 20:28; 2 Samuel 5:23) etc., to suppose that the answer was given simply by the word of the Lord to the high priest comp. (John 11:51) when, clothed with the ephod and the breastplate, he had inquired of the Lord. Such a view agrees with the true notion of the breastplate.