Augustine of Hippo — as excerpted in the Catena Aurea on John 3:27-30

“(Tr. xxv. c. 4, 5) What meaneth this, He must increase? God neither increases, nor decreases. And John and Jesus, according to the flesh, were of the same age: for the six months’ difference between them is of no consequence. This is a great mystery. Before our Lord came, men gloried in themselves; He came in no man’s nature, that the glory of man might be diminished, and the glory of God exalted. For He came to remit sins upon man’s confession: a man’s confession, a man’s humility, is God’s pity, God’s exaltation. This truth Christ and John proved, even by their modes of suffering: John was beheaded, Christ was lifted up on the cross. Then Christ was born, when the days begin to lengthen; John, when they begin to shorten. Let God’s glory then increase in us, and our own decrease, that ours also may increase in God. But it is because thou understandest God more and more, that He seemeth to increase in thee: for in His own nature He increaseth not, but is ever perfect: even as to a man cured of blindness, who beginneth to see a little, and daily seeth more, the light seemeth to increase, whereas it is in reality always at the fall, whether he seeth it or not. In like manner the inner man maketh advancement in God, and it seemeth as if God were increasing in Him; but it is He Himself that decreaseth, falling from the height of His own glory, and rising in the glory of God.”