You are also to make a breastpiece of judgment with the same workmanship as the ephod. Construct it with gold, with blue, purple, and scarlet yarn, and with finely spun linen.
The most considerable of the ornaments of the high priest was this breast-plate, a rich piece of cloth, curiously wrought with gold and purple, etc., two spans long and a span broad, so that, being doubled, it was a span square, Exo 28:16.
Commenting on Exodus 28:15-30
Four square it shall be, being doubled,.... That is, when it was doubled; for the length of it, according to Maimonides (c), was a cubit, which is two spans, and so, when it was doubled, was but one, and its length and breadth being alike, as follows: a span shall be the length thereof, and a span shall be the breadth thereof; a square, which...
thou shalt make the breastplate of judgment with cunning work--a very splendid and richly embroidered piece of brocade, a span square, and doubled, to enable it the better to bear the weight of the precious stones in it. There were twelve different stones, containing each the name of a tribe, and arranged in four rows, three in each.