Exodus 39:7

And he put them on the shoulders of the ephod, that they should be stones for a memorial to the children of Israel; as the Lord commanded Moses.

Cross-references

Exodus 28:12 commands placing the onyx stones on the ephod's shoulders — here that command is fulfilled.

Exodus 28:29 describes the breastplate as a memorial on Aaron's heart — the shoulder stones here also serve as a memorial.