John the Baptist is saying that God is the author of all that we receive. So John is content to see Jesus receive the greater honour that the Father bestowed on Him. So he says, “He must increase, but I must decrease”. These words are also instructive to us that are believers in Jesus Christ. All Glory must be to the Lord. We live our lives to the Glory of God alone (sola Gloriae Dei). He must increase, we must decrease.