Thomas Hamilton (Exodus) describes the ephod of Aaron: It “is shaped like an apron encircling the body and covers the loins (maybe “from waist to thigh). It is kept in position on the body by means of two shoulder pieces (v. 7) and a fastening band (v. 8).”
The ephod is an exterior garment, worn over the tunic and robe (vv, 31-35, 39). Exodus 28 moves from the priest’s outerwear in, from ephod to robe to tunic, reversing the order of Exodus 26, which describes the tabernacle curtains described from inside out, from tabernacle to goats’ hair to rams’ skins to dugong.
Five materials are woven together to make the ephod: Gold thread, three colors of dyed wool (blue, purple, scarlet), and fine linen. (Milgrom argues the colored thread must be wool because ancient peoples had no dyes that would work on linen.) Five is often associated with military formation, a hint that the priest is robed for a form of liturgical warfare; he wears the armor of God.
It’s possible that gold is listed first because it’s the most abundant material of the ephod. If so, the ephod would be metallic and heavy like a breastplate, especially when the “breast piece of judgment” is added (Exodus 28:15-30). This gives us some hint of how Israel could use an ephod as a focus of idolatrous worship (Judges 8:27; 17:5; 18:14-20). It’s solid, more like a relic or graven statue than a piece of clothing.
Jim Jordan has suggested the colors of the ephod replicate the tabernacle and an order of approach to Yahweh. Blue/violet thread recalls the pale color of incense smoke; purple is the deeper hue of the smoke of the bronze altar, and the animal sacrifices; red stands for blood. In an offering, blood is thrown or smeared on the altar and the animal rises in smoke. His destination is the golden throne of Yahweh. If Jordan is right, Aaron is decked out as a living sacrifice, who is ordained to “ascend” through the veil in order to be a sweet savor to Yahweh.
More generally, there are visual links between fire and the colors of the ephod (and breast piece). When Aaron worked in the court, the sunlight would glint off his golden garments, as if he were a living lampstand. His clothing also replicated Yahweh’s cloud-and-fire glory (Kline, Images of the Spirit). Aaron is a likeness to the glory.
Four of the five materials are used for the tabernacle, the innermost curtain of the tent of meeting: linen, along with blue, purple, and scarlet wool (Exodus 26:1). There is no gold, and the order again is perhaps significant: The curtains are mostly white fine linen. The tabernacle is the first of the tent curtains described in Exodus 26, followed by several layers of curtains made from other materials, which were placed on top of the tabernacle.
That order and those materials give us a hint about the meaning of the priestly garments: Aaron is robed in a human-sized replica of the tabernacle, but his outer garments display the hidden interior of the tent. Israel glimpses the Holy Place they never enter every time they look at Aaron. He’s a living tabernacle, and the gold of his ephod links him with the gold lampstand, table, and altar of the Holy Place. Robed in the ephod, Aaron is glorified and sanctified to become a permanent furnishing of Yahweh’s house.
The word ephod is used 12x in Exodus 28 (28:4, 6, 12, 15, 25, 26, 27 [2x], 28 [3x], 31), one of many indications that the priest in his priestly robes embodies the twelve tribes. The onyx stones at the shoulders of the ephod are an explicit sign of the priest’s representative role.
In fact, most of the instructions about the ephod is taken up with the design of the stones. Six of the nine verses are devoted to the stones and their settings, arranged in a parallel pattern:
A. Stones engraved with names, vv. 9-11a
B. Settings, v. 11b
A’. Stones as memorial, v. 12
B’. Chains and settings, vv. 13-14
Section A itself is a twisted knot:
A. Two onyx stones, v 9a
B. Engrave names, v. 9b
B’. Six names on each, v. 10
A’. Engrave two stones, v. 11a
C. Settings of gold, v. 11c
The stones are set in golden settings, with golden chainwork, on the shoulders of the ephod. They are engraved with the names of the sons of Israel, in birth order (Exodus 28:9-10). The phrasing suggests that the names are the names of the sons, not of the tribes (hence, Joseph instead of Manasseh and Ephraim), in contrast to the names on the gemstones of the breast piece, which are inscribed with the names of the “twelve tribes” (Exodus 28:21).
The purpose of the stones is explicit in verse 12: They are a “memorial” (zikkaron) before Yahweh, like the stones of the breast piece (Exodus 28:29), Passover (Exodus 12:14), the silver trumpets (Numbers 10:10). Memorials are directed toward Yahweh, reminders of his promises to Israel. Aaron carries Israel on his shoulders; he shoulders responsibility for Israel’s health and future. But they depend on him because he bears Israel’s names before Yahweh in his house.