What is the role of John the Baptist in John's gospel?

'There was a man sent from God, whose name was John. He came as a witness, to bear witness about the light, that all might believe through him. He was not the light, but came to bear witness about the light.' (Jn 1:6-8)

In the Prologue to his gospel, John emphasises that John the Baptist was 'sent from God' as a 'witness' to Jesus Christ, described as the 'Word' and the 'light'. The Old Testament law stated that a matter must be established by two or three witnesses, and John the Baptist is one of several witnesses to Jesus Christ's identity and salvation purpose in the gospel. 'John bore witness about him, and cried out, "This was he of whom I said, 'He who comes after me ranks before me, because he was before me.'" (Jn 1:15) John's words show that he wants the people to understand that Jesus is greater than himself. They even hint at Christ's divinity, being 'before' him, which links with Jesus' statement later on in the gospel that 'before Abraham was, I am'.

John tells the Jewish authorities plainly, "I am not the Christ." (Jn 1:20). Instead, he identifies himself with the figure Isaiah prophesied: 'the voice of one crying out in the wilderness, 'Make straight the way of the Lord' (Jn 1:23). He acts as a servant of the Lord who prepares the way for His coming. His baptizing people symbolises a call for them to repent and be ready to greet the Lord when He comes. Jesus Himself submitted to be baptized by John, and John testifies "I saw the Spirit descend from heaven like a dove, and it remained on him." (Jn 1:32) This is confirmation that Jesus is the 'Son of God' (Jn 1:34).

Significantly, John gives Jesus the title 'the Lamb of God, who takes away the sin of the world!' (Jn 1:29). This name clearly links Jesus with several important Old Testament images. Firstly, the Passover lamb, slain as a substitute so that the firstborn son would not die in the Israelite household. The blood over the doorpost protected the family from the angel of death. John refers to several Passover festivals in his gospel, and emphasises that Christ's death occurs at the time of the Passover, completing the sense of symbolism that Christ fulfils the Passover by dying as a sacrifice, or a substitute, for God's people.

When the law of Moses was given, a levitical priesthood was established where unblemished lambs were offered as sin offerings on behalf of the people, continuing the Passover tradition. John therefore clearly understood Jesus' role was to bring salvation to God's people by dying in their place.

John the Baptist remains an inspirational figure to imitate, as he shows deep humility. When his disciples leave him to follow Jesus, he accepts this as the right course of action: "The friend of the bridegroom, who stands and hears him, rejoices greatly at the bridegroom’s voice. Therefore this joy of mine is now complete. He must increase, but I must decrease." (Jn 3:29-30) If we see John the Baptist as a peripheral figure in John's gospel, that is how he would have wanted it to be. For John the apostle and John the Baptist, the real focus had to be on Jesus, because 'Whoever believes in the Son has eternal life;whoever does not obey the Son shall not see life, but the wrath of God remains on him.' (Jn 3:36)