The artisans made the forehead-plate, and inscribed upon it "Holy unto G-d."
The high priest was required to wear the Forehead-plate because the forehead represents stubborn determination. We all naturally wrinkle our forehead muscles whenever we resolve to see something through despite all odds.
Stubbornness can be positive or negative. Brazen nerve or arrogance in showing contempt for G-d's law is negative. It is no coincidence that the stone thrown from David's slingshot hit and killed Goliath in the forehead, for Goliath brazenly and openly defied G-d. We are therefore taught that the high priest's forehead-plate atoned for the sin of arrogance.
An example of positive stubbornness is the resolve that enables us to stay true throughout the day to the spiritual awakening that we feel during our morning prayers. As we go about our daily business, it may be difficult to maintain the heightened Divine consciousness that we aspire to in prayer. But we can certainly maintain the attitude toward life implicit in this heightened awareness: that our Divine mission is our primary concern and the purpose of our involvement in the material world is to elevate is by using it for G-dly purposes.
Our goal of making everything "Holy unto G-d" was therefore inscribed on the Forehead-plate.
Daily Wisdom #1