The twelve stones in the breastplate, with their bright colors, were of great importance in the oracular sentences of the high priest, who by means of these stones made the Urim and Tummim exercise their functions. For whenever the king or the head of the Sanhedrin wished to get directions from the Urim and Tummim he betook himself to the high priest. The latter, robed in his breastplate and ephod, bade him look into his face and submit his inquiry.
The high priest, looking down on his breastplate, then looked to see which of the letters engraved on the stones shone out most brightly, and then constructed the answer out of these letters. Thus, for example, when David inquired of the Urim and Tummim if Saul would pursue him, the high priest Abiathar beheld gleaming forth the letter Yod in Judah's name, Resh in Reuben's name, and Dalet in Dan's name, hence the answer read as follows: Yered, "He will pursue."