We sometimes refer to the sun and the moon as the “greater light” and the “lesser light” respectively (from Genesis 1:16). Looking at how those lights work is a neat little metaphor for Christian life.
The greater light, or the sun, has light in itself. The lesser light, the moon, does not, it merely reflects the radiance of the greater light. Any light that the moon has comes from the sun.
As Christians, any light that comes off of us is not actually from us. It is God’s light reflecting off of us. We are lesser lights merely reflecting the radiance of the Greater Light. Jesus, the Son of God, is the light of the world (John 8:12, 9:5, and 12:46), and we are called to be lights in the world (Matthew 5:14-16). We are little moons reflecting the Sonlight.