The breastplate was a pocket of material of the same fabric as the ephod. Twelve precious stones fastened to the front of it, and two objects, the Urim and Thummim that were probably stones also, lay within it.
The 12 jewels represented the 12 tribes. Each one was unique. God later called the Israelites His jewels (Mal. 3:17). The high priest carried the tribes on his heart (v. 30) as well as on his shoulders. The heart refers to the seat of feelings and affections in the Old Testament.
"The purpose of the breastpiece was for making decisions' (v. 15). The Urim and Thummim, deposited in the pouch, were sacred lots used as the means of making decisions' (v. 30). The word Urim' begins with the first letter of the Hebrew alphabet and Thummim' begins with the last letter, so the lots were probably restricted to giving either positive or negative responses to questions asked of them. Strengthening that likelihood is the fact that the phrase Urim and Thummim' is best translated into English as curses and perfections,' meaning that if Urim' dominated when the lots were cast the answer would be no but if Thummim' dominated the answer would be yes."475
