Sefer HaChinuch ספר החינוך

That the breastplate not move from on top of the apron: That we not move the breastplate from on top of the apron. And above we have already mentioned the matter of the breastplate and the apron, which are two of the eight clothes of the high priest. And the breastplate was set in line [and] in front of the heart of the priest. And the apron is behind him across from the breastplate that is in front of him. And there was within the apron, from the cloth of the apron itself, like a type of two handles that come out from it, that the priest girds himself with; and it is called the band (cheshev) of the apron. And after he girds himself with the band of the apron, and placed the breastplate on his heart, it would sit under the breastplate. And Scripture commanded to tie rings that were fixed onto the breastplate and rings that were fixed onto the apron with a string of blue (tekhelet), so that the breastplate would be set upon the band in a fixed and dignified way. As if he did not tie them with those rings, the breastplate would wander and be separated from the band of the apron and bang upon the chamber of the priest’s heart. And about this is it stated (Exodus 28:28), “and the breastplate shall not budge from the apron” — meaning to say from upon the band of the apron. And its [official Aramaic] translation (Onkelos) is to break apart (yitparak). And one who severs its connection at the time of the service is lashed for this negative commandment.

It is from the roots of the commandment that God, may He be blessed, wanted for our good to bring us merit by the aggrandizement of that holy house, [such that] everything in it be proper and set in its place. Whether in the matter of its vessels, that they should be completely perfect, or whether in the matter of the vessels of its servants — such as these clothes that they wear at the time of the service — everything should be proper and completely perfect. No beauty should be lacking from any of [these] things. And in truth, it is from the beauty of the matter that the breastplate should not be loose and wandering upon the chamber of his heart, but it should rather sit fixed like a type of [thing set in] plaster. And we will hold to this [explanation], until we hear better than it.

The laws of the commandment — for example, the design of the breastplate and the apron; the order of their being adorned; and the rest of its details — are elucidated in Middot.

And this commandment that we not remove the breastplate from the apron is practiced at the time of the [Temple] by males and females. [This] means to say that it is the same; [both] a man or a woman that severs their connection is lashed.