What is the Breastplate?
1. A part of the official dress of the Jewish high priest. Ex 28:15. It was a piece of embroidered work, about 10 inches square and made double, with a front and lining, so as to answer for a pouch or bag. It was adorned with twelve precious stones. See High Priest. The two upper corners were fastened to the ephod, from which it was not to be loosed, Ex 28:28, and the two lower corners to the girdle. The rings, chains, and other fastenings were of gold or rich lace. It was called the memorial, Ex 28:12, 1 Chr 2:29, inasmuch as it reminded the priest of his representative character in relation to the twelve tribes; and it is also called the breastplate of judgment, Ex 28:15, perhaps because it was worn by him who was instrumentally the fountain of justice and judgment to the Jewish Church. Others think it is because the Urim and Thummim were annexed to it. See Urim and Thummim. 2. The breastplate was also that article of ancient armor which protected the breast. Eph 6:14. See Armor. Its figurative use in the passage above cited, and also in Isa 69:17, is sufficiently obvious.
Bibliography Information Schaff, Philip, Dr. "Biblical Definition for 'breastplate' in Schaffs Bible Dictionary". bible-history.com - Schaff's