Charles Ellicott Commentary Exodus 28:12

"And thou shalt put the two stones upon the shoulder-pieces of the ephod, to be stones of memorial for the children of Israel: and Aaron shall bear their names before Jehovah upon his two shoulders for a memorial." — Exodus 28:12 (ASV)

For stones of memorial to the children of Israel. —Rather, for the children of Israel. The intention was that the stones should be “stones of memorial” to God, on behalf of Israel; they should remind God that the high priest represented all the tribes, and pleaded before Him on their behalf, and in their name. The tribes were represented doubly in the costume of the high priest, by the onyx stones and by the stones of the breastplate.