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The ephod first appears in the Bible as a garment made to be worn by Aaron the High Priest.
Exodus 28:4 "And these are the garments which they shall make: a breastplate, an ephod, a robe, a skillfully woven tunic, a turban, and a sash. So they shall make holy garments for Aaron your brother and his sons, that he may minister to Me as priest... 6 "and they shall make the ephod of gold, blue, purple, and scarlet thread, and fine woven linen, artistically worked. 7 "It shall have two shoulder straps joined at its two edges, and so it shall be joined together.... 12 "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.
A breastplate with 12 precious stones (engraved with the names of the tribes of Israel) was fastened to it.
Exodus 28:15 "You shall make the breastplate of judgment. Artistically woven according to the workmanship of the ephod you shall make it: of gold, blue, purple, and scarlet thread, and fine woven linen, you shall make it... 22 "You shall make chains for the breastplate at the end, like braided cords of pure gold. 23 "And you shall make two rings of gold for the breastplate, and put the two rings on the two ends of the breastplate. 25 "and the other two ends of the two braided chains you shall fasten to the two settings, and put them on the shoulder straps of the ephod in the front. 26 "You shall make two rings of gold, and put them on the two ends of the breastplate, on the edge of it, which is on the inner side of the ephod. 27 "And two other rings of gold you shall make, and put them on the two shoulder straps, underneath the ephod toward its front, right at the seam above the intricately woven band of the ephod. 28 "They shall bind the breastplate by means of its rings to the rings of the ephod, using a blue cord, so that it is above the intricately woven band of the ephod, and so that the breastplate does not come loose from the ephod.
The breastplate contained the Urim and Thummim which were used to enquire of God. The answers to such enquiries would seem to have been in the form of a straight ‘yes’ or ‘no’. Whether the Urim and Thummim consisted of a black and white stone pulled at random from the pouch of the breastplate or the answers came in some other way we do not know. Leviticus 8 describes Aaron being clothed with the garments.
Leviticus 8:7 And he (Moses) put the tunic on him (Aaron), girded him with the sash, clothed him with the robe, and put the ephod on him; and he girded him with the intricately woven band of the ephod, and with it tied the ephod on him. 8 Then he put the breastplate on him, and he put the Urim and the Thummim in the breastplate.
In the time of Saul the priest at Shiloh wore the ephod.
1 Samuel 14:3 Ahijah the son of Ahitub, Ichabod’s brother, the son of Phinehas, the son of Eli, the LORD’S priest in Shiloh, was wearing an ephod...
Saul was in process of making enquiry by it (we assume by the urim and thummim in the breastplate on the ephod) via the priest when events caused him to abort the enquiry.
1 Samuel 14:19 Now it happened, while Saul talked to the priest, that the noise which was in the camp of the Philistines continued to increase; so Saul said to the priest, "Withdraw your hand."
When Saul slaughtered the priests, Abiathar escaped and went to David taking the ephod and David made enquiry of God by it.
1 Samuel 23:6 Now it happened, when Abiathar the son of Ahimelech fled to David at Keilah, that he went down with an ephod in his hand... 9 When David knew that Saul plotted evil against him, he said to Abiathar the priest, "Bring the ephod here."
Beside the High Priest’s ephod, other ephods (without a breastplate) would seem to have been made and worn.
Samuel wore an ephod.
1 Samuel 2:18 But Samuel ministered before the LORD, even as a child, wearing a linen ephod.
David wore an ephod.
2 Samuel 6:14 Then David danced before the LORD with all his might; and David was wearing a linen ephod.
In a way which is not clear other ephods were made which became part of idolatrous worship.
Judges 8:27 Then Gideon made it into an ephod and set it up in his city, Ophrah. And all Israel played the harlot with it there. It became a snare to Gideon and to his house.
Judges 17:5 The man Micah had a shrine, and made an ephod and household idols; and he consecrated one of his sons, who became his priest.
The ephod of the high priest was the means whereby Israel could communicate with God. When they turned to Idolatry God said that they would be deprived of this means of direct communication along with a king, the means of sacrifice (Temple and altar) and their idols for many days.
AV Hosea 3:4 For the children of Israel shall abide many days without a king, and without a prince, and without a sacrifice, and without an image, and without an ephod, and without teraphim:
When they returned from the Babylonian captivity they were ‘cured’ of idolatry but they no longer had a king or the ephod of the High Priest with the Urim and Thummim. Because no direct enquiry could be made of God, the priests who could not prove their genealogy were barred from the priesthood.
AV Nehemiah 7:65 And the Tirshatha said unto them, that they should not eat of the most holy things, till there stood up a priest with Urim and Thummim.
When Christ returns to restore the kingdom to Israel this deficiency will be rectified.
Malachi 3:3 He will sit as a refiner and a purifier of silver; He will purify the sons of Levi, And purge them as gold and silver, That they may offer to the LORD An offering in righteousness.
The meaning of Urim and Thummim in Hebrew is ‘lights’ and ‘perfections’ the antitype of which is Christ; the light of the world, perfect in all his ways.