38 It shall be on Aaron's forehead, and Aaron shall take on himself any guilt incurred in the holy offering that the Israelites consecrate as their sacred donations; it shall always be on his forehead, in order that they may find favor before the Lord.

Matthew Henry's Commentary on Exodus 28:38

Commentary on Exodus 28:31-39

(Read Exodus 28:31-39)

The robe of the ephod was under the ephod, and reached down to the knees, without sleeves. Aaron must minister in the garments appointed. We must serve the Lord with holy fear, as those who know they deserve to die. A golden plate was fixed on Aaron's forehead, engraven with "Holiness to the Lord." Aaron was hereby reminded that God is holy, and that his priests must be holy, devoted to the Lord. This must appear in their forehead, in open profession of their relation to God. It must be engraven like the engravings of a signet; deep and durable; not painted so as to be washed off, but firm and lasting; such must our holiness to the Lord be. Christ is our High Priest; through him sins are forgiven to us, and not laid to our charge. Our persons, our doings, are pleasing to God upon the account of Christ, and not otherwise.