From: John 3:22-30
John Again Bears Witness
 After this Jesus and his disciples went into the land of Judea; there he remained with them and baptized.  John also was baptizing at Aenon near Salim, because there was much water there; and people came and were baptized.  For John had not yet been put in prison.
 Now a discussion arose between John's disciples and a Jew over purifying.  And they came to John, and said to him, Rabbi, he who was with you beyond the Jordan, to whom you bore witness, here he is, baptizing, and all are going to him."  John answered, "No one can receive anything except what is given him from heaven.  You yourselves bear me witness, that I said, I am not the Christ, but I have been sent before him.  He who has the bride is the bridegroom; the friend of the bridegroom, who stands and hears him, rejoices greatly at the bridegroom's voice; therefore this joy of mine is now full.  He must increase, but I must decrease.
22-24. A little later on (Jn 4:2) the evangelist makes it clear that it was not Jesus himself who baptized, but his disciples Our Lord probably wanted them from the very beginning to get practice in exhorting people to conversion. The rite referred to here was not yet Christian Baptism--which only began after the resurrection of Christ (cf. Jn 7:39; 16:7; Mt 28:19)--but "both baptisms, that of St John the Baptist and that of our Lord's disciples [...], had a single purpose--to bring the baptized to Christ [...] and prepare the way for future faith" (St John Chrysostom, "Hom. on St John", 29, 1).
The Gospel gives the exact time and place of this episode. Aenon is an Aramaic word meaning "wells". Salim was situated to the north-east of Samaria, south of the town of Scythopolis or Beisan, near the western bank of the Jordan, about twenty kilometers (thirteen miles) to the south of the Lake of Gennesaret.
The Gospel notes that "John had not yet been put in prison" (v. 24), thus rounding out the information given by the Synoptics (Mt 4:12; Mk 1:14). We know, therefore, that Jesus' public ministry began when John the Baptist's mission was still going on, and, particularly, that there was no competition of any kind between them; on the contrary, the Baptist, who was preparing the way of the Lord, had the joy of actually seeing his own disciples follow Jesus (cf. Jn 1:37).
27-29. John the Baptist is speaking in a symbolic way here, after the style of the prophets; our Lord himself does the same thing. The bridegroom is Jesus Christ. From other passages in the New Testament we know that the Church is described as the Bride (cf. Eph 5:24-32; Rev 19:7-9). This symbol of the wedding expresses the way Christ unites the Church to himself, and the way the Church is hallowed and shaped in God's own life. The Baptist rejoices to see that the Messiah has already begun his public ministry, and he recognizes the infinite distance between his position and that of Christ: his joy is full because he sees Jesus calling people and them following him.
"The friend of the bridegroom", according to Jewish custom, refers to the man who used to accompany the bridegroom at the start of the wedding and play a formal part in the wedding celebration--the best man. Obviously, as the Baptist says, there is a great difference between him and the bridegroom, who occupies the center of the stage.
30. The Baptist knew his mission was one of preparing the way of the Lord; he was to fade into the background once the Messiah arrived, which he did faithfully and humbly. In the same way, a Christian, when engaged in apostolate, should try to keep out of the limelight and allow Christ to seek men out; he should be always emptying himself, to allow Christ fill his life. "It is necessary for Christ to grow in you, for you to progress in your knowledge and love of him: for, the more you know him and love him, the more he grows in you. [...] Therefore, people who advance in this way need to have less self-esteem, because the more a person discovers God's greatness the less importance he gives to his own human condition" (St Thomas Aquinas, "Commentary on St John, in loc.").
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.