Trim And Thummim (Heb. Urim Light; Tummim Truth Or Perfection) a part of the breast apparel of the high priest among the ancient Hebrews. According to one opinion, they denote the four rows of brilliant precious stones in the breastplate of the high priest, upon each of which was engraved the name of one of the sons of Israel. When an appeal was made to God by the high priest in difficult cases, the divine answer was manifested in some way by means of this breastplate, or, in the opinion of some commentators, by an audible voice speaking to the priest arrayed in full pontificals. According to others, the Urim and Thummim were two images personifying revelation and truth placed between the folds of the breastplate. The first time they, are mentioned in the Bible, they are referred to as things already familiar to the Israelites: " And thou shalt put in the breastplate of judgment the Urim and the Thummim." (Exod. xxviii. 30.) It is unknown when this oracular method of consulting God ceased. There is no instance of it in Scripture during the time of the first temple, and it certainly was not practised during that of the second.
There is a rabbinical saying that God spoke to his people during the tabernacle by the Urim and Thummim, during the first temple by the prophets, and during the second by the Bath-Kol.