Exodus 28:15

15Likewise, you shall make the breastplate of judgment, wrought with diverse colors according to the weaving of the ephod: of gold, hyacinth and purple, and twice-dyed scarlet, and fine twisted linen.
28:15 The rational of judgment: This part of the 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 the 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.(Challoner)
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