This formed part of the High Priest's dress, and no doubt, like the office itself, was intended as typical of Christ. It was a rich dress composed of different colours, blue, purple, and crimson, and adorned with gold. On that part of it which crossed the breast was a square ornament called the choschen, containing precious stones, with the names on them of the twelve tribes of Israel. Nothing could more aptly represent our great High Priest, the Lord Jesus Christ, going in before the presence of JEHOVAH with the names of his people on his breast. Hence the church, in allusion to it, vehemently urgeth Christ in that request, "Set me as a seal upon thine heart, as a seal upon thine arm;" (Song of Song of Solomon 8:6) meaning, that she might be always in his remembrance, to live in his heart, and to be always looked upon as a seal, or signet, on the arm. (See Exodus 28:4-29)
See Urim and Thummim