Exodus 28:30

את האורים ואת התמים THE URIM AND THE THUMMIM — This was an inscription of the Proper Name of God which was placed between the folds (i. e. the two pieces forming the front and back) of the breast-plate through which it (the breast-plate) made its statements clear (lit., illuminated its words; מאיר from אור, light, this being an allusion to the אורים) and its promises true (מתמם from the root תמם, an allusion to תמים) (Yoma 73b). In the second Temple there was certainly the breast-plate (although other objects employed in the Temple Service were missing) for it was impossible that the High Priest should have lacked a garment, but that Divine Name was not within it. It was on account of the inscription which constituted the Urim and Thummim and which enabled it to give decisions that it was called “judgment”, as it is said, (Numbers 27:21) “And he shall enquire for him by the judgment of the Urim” (Numbers 27:21). את משפט בני ישראל [AND AARON SHALL BEAR] THE JUDGMENT OF THE CHILDREN OF ISRAEL — the object by means of which they are judged and admonished whether they should do a particular thing or whether they should not do it. But according to the Midrashic statement (Zevachim 88b) that the breast-plate atoned for those who pervert judgment it was called “judgment” in allusion to the pardon thus given for perverse judgment.

וְנָתַתָּ֞ אֶל־חֹ֣שֶׁן הַמִּשְׁפָּ֗ט אֶת־הָאוּרִים֙ וְאֶת־הַתֻּמִּ֔ים וְהָיוּ֙ עַל־לֵ֣ב אַהֲרֹ֔ן בְּבֹא֖וֹ לִפְנֵ֣י יְהֹוָ֑ה וְנָשָׂ֣א אַ֠הֲרֹ֠ן אֶת־מִשְׁפַּ֨ט בְּנֵי־יִשְׂרָאֵ֧ל עַל־לִבּ֛וֹ לִפְנֵ֥י יְהֹוָ֖ה תָּמִֽיד׃ {ס}        

And thou shalt put in the breastplate of judgment the Urim and the Tummim; and they shall be upon Aharon’s heart, when he goes in before the Lord: and Aharon shall bear the judgment of the children of Yisra᾽el upon his heart before the Lord continually.