A.B. Simpson emphasizes that just as jewels require light to reveal their beauty, so do we need the light of God to reflect our true worth. He illustrates that without God's illumination, we remain in a crude state, lacking the ability to showcase the beauty of Christ within us. The sermon encourages believers to recognize their identity as chosen people, called to display the excellencies of Jesus, who brings us out of darkness into His marvelous light. Simpson urges us to allow God's light to shine through us, reflecting His love and beauty to the world.