First of all, it implies a progressive “seeing” process as depicted in John 1: 29-34. The verb “to see” in English repeated four times is the translation of four Greek roots: blepo, theaomai, theoreo, and horao. This seeing process begins with a general level of observation which progressively becomes mediation, contemplation, experience of identification, and finally the inner compulsion demanding witness (Cf. 1Jn 1: 1-4). Finally John the Baptist says, “I have seen” and hence cannot but gives witness. So the authentic witness is the result of deeper inner experience and the consequent conviction.
The content of the witness of John the Baptist is: “Behold the lamb of God who takes away the sins of the world.” It is to be observed that the Aramaic word for “lamb” is thelya and it has also the meaning “servant”. This brings out two essential background images of the text, namely, the Passover lamb (Ex 12) and the suffering servant o Yahweh in Isaiah (Is 42 onwards). So John the Baptist points to Jesus as the one through whom God will save the world from the slavery of sin. Jesus is the new Passover lamb. Jesus is also the one who will become the ransom for the salvation of the world, voluntarily accepting the world’s suffering on himself.
In John 3: 22-30 this witness of John the Baptist is further clarified through a beautiful imagery of “friend of the bridegroom”. John the Baptist is answering a question put by his disciples as to who is greater, John the Baptist or Jesus? John the Baptist is confirming the witness he gave in Chapter one of John’s Gospel and identifies Jesus as the bridegroom who has the bride and himself as the friend of the bridegroom. The main theme is evidently that of the covenantal relationship for which the imagery of wedding is used in the Old Testament. So John the Baptist confirms that the ministry of Jesus is the establishment of the new covenant, and Jesus is in the place of God. His own function is identified as the preparation for this new relationship between God and the people.
A friend of the bridegroom is usually entrusted with the organization of the wedding. The bridegroom trusts his best friend. The responsibility of the friend ends only with the union of bridegroom and bride in the wedding chamber. As the friend is waiting, he hears the voice of the bridegroom from the wedding chamber expressing his joy over the virginal bride and the friend is happy because his responsibility has been perfectly fulfilled. Some think that the voice heard by the friend is that of the procession bringing the bridegroom. In that case too, he is happy because the bridegroom has arrived and his responsibility is over. Hence “he must increase, I must decrease.” John the Baptist must disappear from the scene as more and more people go to Jesus and become part of the new community. This increase is reported later in John 10: 40-42. An authentic witness of Christ should in no way project himself to the world. He has to build the bridge to Christ and disappear from the stage.