Exodus 28:15

The rational of judgment. This part of the high priest's attire, which he wore at his breast, was called the rational of judgment; partly because it admonished both priest and people of their duty to God; by carrying the names of all their tribes in his presence; and by the Urim and Thummim, that is, doctrine and truth, which were written upon it: and partly because it gave divine answers and oracles, as if it were rational and endowed with judgment.