שמות כח:יב פירוש: רש״י, ספורנו, רשב״ם והעמק דבר

לזכרון FOR A MEMORIAL — so that the Holy One, blessed be He, will see the names of the tribes written before Him and He will remember their righteousness (cf. Exodus Rabbah 38:8).

על שתי כתפיו לזכרון, in order to attract the attribute of Mercy to be invoked by their merit. (the merit of wearing the shoulder pads)

על כתפות האפוד. These shoulder pads of the ephod extended from his shoulder on either side up to the neck of the High Priest, from which point they curved and descended towards the breastplate he wore on the chest. There were chains which linked the ephod to the breastplate, and the two major gemstones known as אבני זכרון (as well as אבני שהם) that had the names of the tribes engraved on them and which he wore like epaulettes on his two shoulders. The breastplate was suspended from these chains, apart from being fastened additionally to the ephod.