Exodus 28:36

On the golden plate fixed upon Aaron's forehead, like an half coronet, reaching, as the Jews say, from ear to ear, must be engraven, Holiness to the Lord — Aaron must hereby be minded, 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 he 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 he washed off, but sincere and lasting.