Adam Clarke on Exodus 28:15

The breastplate of judgment - חשן משפט choshen mishpat, the same as the חשן choshen, see Exo 25:7, but here called the breastplate of judgment, because the high priest wore it upon his breast when he went to ask counsel of the Lord, to give judgment in any particular case; as also when he sat as judge to teach the law, and to determine controversies. See Lev 10:11; Deu 17:8, Deu 17:9.