The breastpiece receives more attention than any other item. This suggests the breastpiece was very important.
The breastpiece symbolized the priest's representation of Israel (28:17–21, 29). It held the Urim and Thummim, objects through which God revealed his will (28:30).
The high priest had two main tasks. First, he brought the people to God. He represented them before the Lord.
Second, he brought God’s word to the people. He spoke to them on God’s behalf.
The chestpiece stood for both of these duties. It showed that the high priest served as a bridge between God and the people.