Bell
Bells appear in only two settings in the UPDV: as gold ornaments alternating with yarn-pomegranates around the hem of the high priest's blue robe, and — in an eschatological reversal — as the consecrated fittings of cavalry horses on which the priestly inscription HOLY TO YAHWEH is carried out of the sanctuary into the most ordinary war-mount.
On the Hem of the Priestly Robe
The bells are first commanded as part of the high-priestly vestments. On the skirts of the blue robe, pomegranates of blue, purple, and scarlet are to alternate with bells of gold "round about" — "and bells of gold between them round about" (Ex 28:33). The pattern is then specified verse by verse: "a golden bell and a pomegranate, a golden bell and a pomegranate, on the skirts of the robe round about" (Ex 28:34).
When the vestments are made under Bezalel, the command is executed exactly: "they made bells of pure gold, and put the bells between the pomegranates on the skirts of the robe round about, between the pomegranates" (Ex 39:25), "a bell and a pomegranate, a bell and a pomegranate, on the skirts of the robe round about, to minister in; as Yahweh commanded Moses" (Ex 39:26). The repeated phrase "round about" fixes the bells as the full circumference of the hem; the alternation with the pomegranates fixes them as one of two ornaments rather than the ground of the hem.
The Sound of Ministry
The bells are not silent ornaments. Their function is fixed in the same instruction-block: "it will be on Aaron to minister: and its sound will be heard when he goes in to the holy place before Yahweh, and when he comes out, that he will not die" (Ex 28:35). The audible bell-sound accompanies the high priest's entry into and exit from the holy place, and the verse links that sound directly to his preservation in the sanctuary. The robe-bells are thus liturgical signaling devices as much as ornamental ones — Aaron's ministry is heard, not only seen, and the hearing of it is bound to his life.
Bells on Horses — Holy to Yahweh
Zechariah's eschatological vision relocates the priestly holiness-motto onto the most ordinary war-mount. "In that day there will be on the bells of the horses, HOLY TO YAHWEH; and the pots in Yahweh's house will be like the bowls before the altar" (Zec 14:20). The inscription HOLY TO YAHWEH is the same legend the high priest had carried on his forehead-plate; Zechariah moves it onto the bells fastened to cavalry horses. Paired with the equalizing of common cooking-pots and altar-bowls in the same verse, the horse-bells stand for the day in which the boundary between sanctuary and ordinary life dissolves — the high-priestly inscription rides out of the holy place on the bells of the war-horses.