John Calvin Reformed @genevareformer

9. And thou shalt take two onyx-stones. That the connection between the priest and the people might be made more plain, God not only placed on his breast the memorials of the twelve tribes, but also engraved their names on his shoulders.

Matthew Henry Presbyterian @wholebiblehenry

Directions are here given concerning the ephod, which was the outmost garment of the high priest. Linen ephods were worn by the inferior priests, Sa1 22:18. Samuel wore one when he was a child (Sa1 2:18), and David when he danced before the ark (Sa2 6:14); but this which the high priest only wore was called a golden ephod, because there was a great deal of gold woven into it.

Commenting on Exodus 28:6-14

John Gill Reformed Baptist @doctorgill

And thou shall take two onyx stones,.... called from the colour of a man's nail, which they to resemble: the Targums of Onkelos and Jonathan call them stones of beryl, and so the Syriac version; the Septuagint, stones of emerald, and the Arabic version, crystal stones: but, according to Josephus (x), they were sardonyx stones, and in which Brannius (y) thinks he was right: and...