1 This lesson from the holy Gospel shows us the excellency of our Lord Jesus Christ's divinity, and the humility of the man who earned the title of the Bridegroom's friend; that we may distinguish between the man who is man, and the Man who is God. For the Man who is God is our Lord Jesus Christ, God before all ages, Man in the age of our world: God of the Father, man of the Virgin, yet one and the same Lord and Saviour Jesus Christ, Son of God, God and man. But John, a man of distinguished grace, was sent before Him, a man enlightened by Him who is the Light. For of John it is said, “He was not the Light, but that he should bear witness of the Light.” He may himself be called a light indeed, and rightly so; but an enlightened, not an enlightening light. The light that enlightens, and that which is enlightened, are different things: for even our eyes are called lights (lumina), and yet when we open them in the dark, they do not see. But the light that enlightens is a light both from itself and for itself, and does not need another light for its shining; but all the rest need it, that they may shine.
Source: Tractates on the Gospel of John (New Advent)