From my Sunday School notes, inspired heavily by Crispin Fletcher-Louis-
They shall take the gold, blue, purple, and scarlet thread, and the fine linen, and they shall make the ephod of gold, blue, purple, and scarlet thread, and fine woven linen, artistically worked. It shall have two shoulder straps joined at its two edges, and so it shall be joined together. And the intricately woven band of the ephod, which is on it, shall be of the same workmanship, made of gold, blue, purple, and scarlet thread, and fine woven linen.
Then you shall take two onyx stones and engrave on them the names of the sons of Israel: six of their names on one stone and six names on the other stone, in order of their birth. With the work of an engraver in stone, like the engravings of a signet, you shall engrave the two stones with the names of the sons of Israel. You shall set them in settings of gold. And you shall put the two stones on the shoulders of the ephod as memorial stones for the sons of Israel. So Aaron shall bear their names before the LORD on his two shoulders as a memorial. You shall also make settings of gold, and you shall make two chains of pure gold like braided cords, and fasten the braided chains to the settings.
An ephod is usually used to refer to a statue of a god (Judges 17:5; 18:14-20; Hos. 3:4; 2 Kings 23:7), and when the priest is decked out in full regalia, he is an image of God.
The ephod is also a warrior’s garment, and the priest is dressed for war. The priests were also armed with spears, and they could kill anyone who attempted to enter into the holy places.
The Urim and Thummim are famously mysterious, but one of the best explanations comes from James Jordan when he points out that these correspond to the first and last letters of the Hebrew alphabet: aleph and tav. Hebrew often uses the alphabet for ordering and numbering. It does this in Psalm 119 and the book of Lamentations. In Greek the Urim and Thummin would be translated as alpha and omega, the beginning and the end. Jesus takes this imagery upon himself, as he is the great high priest.