The comparison of himself with the friend of the bridegroom, in verse 29, continues the same testimony that the Lord Jesus is the Christ.
By calling himself, in Jn 1:23, "the voice of one crying, Prepare the way of the Lord," Is 40:3, and by likening the Lord to a bridegroom, John points directly to prophetic expressions of the Old Testament.
These include Ezek 16:8; Hos 2:19, 21; Mal 2, and many others. In them Jehovah is depicted as the bridegroom, and the people of the promise as the bride.
"And I will betroth you to Myself forever, and you shall know the Lord," says the prophet Hosea. But in these words of Hosea the Lord was no longer calling to the Jewish people.
He was calling to that Church of God which He created upon the ruins of the ancient Old Testament Church, destroyed by the crimes of a stiff-necked people.
The Christian Church became the bride of Christ. John the Baptist spoke his words by the command of the Holy Spirit: "Of this salvation the prophets have inquired. It was revealed to them that they were serving not themselves but us," 1 Pet 1:10-12.
In those words was the fulfillment of what the prophets had proclaimed: the coming of Jehovah to earth in human flesh and the betrothal of the Church to the divine Bridegroom, whose friend and herald John calls himself.
But it was given to him to understand this: the Lord had appeared on earth, and therefore "his joy was fulfilled." He sees the beginning of the Kingdom of God on earth.
Yet he cannot still comprehend the full greatness of the mystery, which is revealed only after the Resurrection of our Lord Jesus Christ.
Moved by the Spirit of God, John testifies concerning the Lord Jesus that He is truly the Christ. He rejoices greatly, seeing "the salvation of the Lord, which the Lord has prepared before the face of all peoples.
It is a light for revelation to the Gentiles and the glory of the Lord's people Israel," Lk 2:30-32.
With a higher spiritual joy, recognizing and proclaiming the Lord Jesus as Christ a second time, cf. Jn 1:26, 30, he announces that the Lord Jesus must increase, while he, John, must decrease.
For the mission laid upon him by God is drawing to its end. Chrysostom supposes that even the death of John the Baptist was permitted by God so soon in order that all the people's attention might be concentrated on Christ.
He rejoices like Symeon the God-receiver, feeling that the Master is releasing him. He feels that "there is laid up for him the crown of righteousness, which the Lord gives to all who have loved His appearing," 2 Tim 4:8.