The high priest also wore this garment. It was his basic garment over which he put the ephod. It covered him completely so his natural nakedness did not appear (cf. Genesis 3:21). [source][source][source]
God may have intended the pomegranates and bells on the hem of the robe ( Exodus 28:33-34) to remind the Israelites of God"s commandments. The pomegranate was probably a symbol of the spiritually nourishing quality of God"s Word (cf. Proverbs 25:11; Psalm 19:8-11; Psalm 119:25; Psalm 119:43; Psalm 119:50; Deuteronomy 8:3; Proverbs 9:8; Ecclesiastes 12:9-11; Ecclesiastes 12:13). The bell was evidently a symbol of the sounding or proclamation of God"s Word through testimony. [1] Some interpreters have felt pomegranates and bells represented fruitfulness and joy. Others have seen them as representing the fruits and gifts of God"s Spirit. [2][source]
"A popular Jewish interpretation of Exodus 28:35 taught that one end of a long rope should be tied to the high priest"s ankle before he entered the Holy Place. Since his slightest movement would cause the bells to tinkle, the people outside would assume that all was well as long as they could hear them. But if the bells fell silent for a time, the people outside would naturally assume that their priest had either fainted or died. They would then tug on the end of the rope to pull him out, making it unnecessary for unauthorized persons to enter the Holy Place in order to remove his body." [3][source]