We have looked at the Ephod the High Priest wore. It had two parts, a front and a back, that were fastened with two shoulder pieces with straps of braided chain of gold and held to the body with a beautiful woven belt at the waist. On the shoulders were two onyx stones with the names of Israel’s tribes: 6 on each stone. When Aaron, the High Priest would enter the Tabernacle, he would be bearing Israel’s name before God.
“You are to make an embroidered breastpiece for making decisions. Make it with the same workmanship as the ephod; make it of gold, of blue, purple, and scarlet yarn, and of finely spun linen. It must be square and folded double, nine inches long and nine inches wide. Place a setting of gemstones on it, four rows of stones: The first row should be row of carnelian, topaz, and emerald; the second row, a turquoise, a sapphire, and a diamond the third row, a jacinth, an agate, and an amethyst; and the fourth row, a beryl, an onyx, and a jasper. They should be adorned with gold filigree in their settings. The 12 stones are to correspond to the names of Israel’s sons. Each stone must be engraved like a seal, with one of the names of the 12 tribes.” Exodus 29:15-21 HCSB
The High Priest’s Breastpiece was to be made from the same cloth as the Ephod and was to be a 9” square folded double to make a “pocket” with 12 precious stones mounted in gold settings; four rows of 3 stones each. Each stone had a name of a tribe of Israel engraved on it. Each stone was a precious gem.
“You are to make braided chains of pure gold cord work for the breastpiece. Fashion two gold rings for the breastpiece and attach them to its two corners. Then attach the two gold cords to the two gold rings at the corners of the breastpiece. Attach the other ends of the two cords to the two filigree settings, and in this way attach them to the ephod’s shoulder pieces in the front. Make two other gold rings and put them at the two other corners of the breastpiece on the edge that is next to the inner border of the ephod. Make two more gold rings and attach them to the bottom of the ephod’s two shoulder pieces on its front, close to its seam, and above the ephod’s woven waistband. The craftsmen are to tie the breastpiece from its rings to the rings of the ephod with a cord of blue yarn, so that the breastpiece is above the ephod’s waistband and does not come loose from the ephod” Exodus 28:22-28 HCSB
The Breastpiece was attached snugly over the Ephod by four gold chains. Two of the chains were slipped through gold rings at the upper corners of the Breastpiece and attached to the Ephod’s shoulder pieces. The other two gold chains were slipped through gold rings at the lower corners of the Breastpiece; attached to the side seams of the ephod and tied with a blue cord to the belt at the waist.
“Whenever he enters the sanctuary, Aaron is to carry the names of Israel’s sons over his heart on the breastpiece for decisions, as a continual reminder before the Lord. Place the Urim and Thummim in the breastpiece for decisions, so that they will also be over Aaron’s heart whenever he comes before the Lord. Aaron will continually carry the means of decisions for the Israelites over his heart before the Lord.” Exodus 28:29-30
The Breastpiece over Aaron’s heart (which is mentioned three times in these verses) was to serve as a continual memorial before the LORD. Another purpose for the Breastpiece was carrying the Urim and the Thummim, which were used by the priests to make decisions for the Israelites. They were held always in the “pocket” formed by the Breastpiece.
“The words, Urim and Thummim means “lights” and “perfections” and are referred to in Numbers 27:21, 1 Samuel 30:7-8, Ezra 2:63 and Nehemiah 7:65 . They were means of seeking from God through the priest answers to questions and crises beyond human perception. Apparently the Urim and Thummim were two stones. How they were used in determining God’s will is unknown, but some suggest the Urim represented a negative answer and the Thummim represented a positive answer. Perhaps this view is indicated by the fact that Urim begins with the first letter of the Hebrew alphabet, and Thummim with the last letter.” The Bible Knowledge Commentary p152