Sforno on Exodus 28:21/ספורנו על שמות כ״ח:כ״א

1והאבנים תהיין על שמות בני ישראל, as soon as the Israelites when donating these various materials had dedicated them to their sacred purpose, i.e. that their names be inscribed on these gemstones, they became sacred, so that the word תהיין, meaning “they will remain, etc.,” is fully justified.”

2שתים עשרה על שמותם, the Torah emphasises that the number 12 is not arbitrary but represents the names of the 12 tribes, no fewer nor any additional ones. [Joseph is represented by one gemstone not two, and the tribe of Levi was included though they did not share in the distribution of the land of Canaan to the tribes. Ed.]

3פתוחי חותם איש על שמו, this sounds like an instruction to the engraver of these gemstones to have in mind the specific name of the tribe when he engraves letters on the gemstone representing that tribe.