Compare Exodus 39:4. The ephod consisted of two principal pieces of cloth, one for the back and the other for the front, joined together by shoulder straps (see Exodus 28:27 note). Below the arms, probably just above the hips, the two pieces were kept in place by a band attached to one of the pieces. On the respect in which the ephod of the High priest was held, see 1-Samuel 2:28; 1-Samuel 14:3; 1-Samuel 21:9; 1-Samuel 23:6-9; 1-Samuel 30:7. But an ephod made of linen appears to have been a recognized garment not only for the common priests 1-Samuel 22:18, but also for those who were even temporarily engaged in the service of the sanctuary 1-Samuel 2:18; 2-Samuel 6:14; 1-Chronicles 15:27.

It shall have the two shoulder pieces thereof,.... Which were two pieces that joined to the ephod, reaching from the arm holes to the shoulders both on the right and left, coming from before and behind; and meeting on the shoulders, were buttoned with two onyx stones, and covering the shoulders are called by this name:
joined at the two edges thereof; the two edges of the ephod; not sewed thereunto with a needle, as Maimonides (w) and other Jewish writers think, but were woven along with it, and in the weaving was of the same with it:
and so it shall be joined together; that is, the hinder and fore parts of the ephod in the shoulder pieces of it, shall be joined together by the two onyx stones upon them, hereafter mentioned, with which they were buttoned.
(w) Ut supra. (Hilchot Cele Hamikdash, c. 9. sect. 9.)

"Two connecting shoulder-pieces shall it have for its two ends, that it may be bound together." If we compare the statement in Exodus 39:4, - "shoulder-pieces they made for it, connecting; at its two ends was it connected," - there can hardly be any doubt that the ephod consisted of two pieces, which were connected together at the top upon (over) the shoulders; and that Knobel is wrong in supposing that it consisted of a single piece, with a hole cut on each side for the arms to be put through. If it had been a compact garment, which had to be drawn over the head like the robe (Exodus 28:31, Exodus 28:32), the opening for the head would certainly have been mentioned, as it is in the case of the latter (Exodus 28:32). The words of the text point most decidedly to the rabbinical idea, that it consisted of two pieces reaching to about the hip, one hanging over the breast, the other down the back, and that it was constructed with two shoulder-pieces which joined the two together. These shoulder-pieces were not made separate, however, and then sewed upon one of the pieces; but they were woven along with the front piece, and that no merely at the top, so as to cover the shoulders when the ephod was worn, but according to Exodus 28:25 (? 27), reaching down on both sides from the shoulders to the girdle (Exodus 28:8).