Targum Pseudo-Jonathan on Exodus 39:14 tells us something small and enormous at once. The twelve stones of the breastplate were engraved as the engraving of a ring — each tribe's name cut into its own gem "according to his name in the twelve tribes."
Why a signet ring?
A signet was how a king signed his decrees. Pharaoh had placed his signet on Joseph's hand (Genesis 41:42). Ahasuerus sealed his letters with his ring. The meturgeman reaches for this image on purpose. The breastplate, he says, was not merely labeled. It was sealed. Each stone carried a tribe's name the way a royal seal carries the king's authority.
When Aharon wore the choshen into the sanctuary, he was wearing twelve royal seals. The twelve tribes entered the presence of the God of Israel not as subjects pleading for admittance but as princes whose names were already signed into the divine record.
One name, one gem
The targumist stresses: each man's gem according to his name. Reuben did not share a stone with Shimeon. Levi did not share with Judah. The tribes were together — all twelve on one garment — but each one was also fully itself. Unity, in the breastplate's logic, is not uniformity. It is twelve distinct lights, each engraved so precisely that the letters could not be mistaken for any other.
The rabbis taught that when the High Priest sought guidance through the Urim v'Tumim, the letters on the stones would brighten in sequence. That answer was only possible because every name had been cut into its own stone. Blurred letters could not have spoken.
The takeaway: the God of Israel does not deal with crowds. Every tribe, every family, every soul is engraved as cleanly as a signet.