Exodus 28:15
And thou shalt make the breastplate of judgment with cunning work; after the work of the ephod thou shalt make it; of gold, of blue, and of purple, and of scarlet, and of fine twined linen, shalt thou make it.
Cross-reference
Exodus 28:4 first lists the breastpiece among priestly garments; here in 28:15 the detailed instructions begin.
Exodus 28:6 describes the ephod made with the same materials — gold, blue, purple, scarlet, and fine linen — showing the breastpiece matches the ephod's design.
Exodus 28:30 directs placing the Urim and Thummim inside the breastpiece described here.
Exodus 28:29 specifies that Aaron carries the names of Israel on the breastpiece over his heart — the same breastpiece's function.
Exodus 39:8 records the actual construction of the breastpiece, fulfilling the instructions given here.
Exodus 25:7 lists precious stones to be set in the ephod and breastpiece — the stones that later decorate the breastpiece (28:17-20).
Exodus 26:1 uses these same colored yarns and fine linen for the tabernacle curtains, linking the priestly garments to the sanctuary's materials.
Exodus 26:31 describes the veil also made of blue, purple, scarlet, and fine linen — the same textile components for the breastpiece.
Exodus 35:6 lists the same materials for the tabernacle — blue, purple, scarlet, fine linen — as used for the breastpiece.
Leviticus 8:8 describes Aaron being clothed with the breastpiece, including the Urim and Thummim, fulfilling these instructions.
Judges 17:5 shows an unauthorized ephod made for idolatry — contrasting with the legitimate priestly breastpiece attached to the ephod.