Exodus 28:36 - Joseph Benson’s Commentary on the Old and New Testaments

On the golden plate fixed upon Aaron's forehead, like a half coronet, reaching, as the Jews say, from ear to ear, must be engraved, Holiness to the Lord Aaron must hereby be reminded, that God is holy, and that his priests must be holy. The high-priest must be consecrated to God, and so must all his ministrations. All that attend in God's house must have holiness to the Lord engraven upon their foreheads, that is, they must be holy, devoted to the Lord, and designing his glory in all they do. This must appear in their forehead, in an open profession of their relation to God, as those that are not ashamed to own it, and in a conversation answerable to it. It must likewise be engraven like the engravings of a signet, so deep, so durable; not painted, so as it may be washed off, but sincere and lasting.