John 1.15

'John bare witness of him, and cried, saying, This was he of whom I spake, He that cometh after me is preferred before me: for he was before.'

John the Baptist was clearly a well known local prophet whilst Jesus was still unknown. When the time of his ministry came Jesus was proclaimed by the Baptist.
What is so important about the baptism that John gave his followers? Before we can receive forgiveness we need to repent. Before we can see our Redeemer we need to acknowledge our servitude.
Often I find with non-Christans that behind the scepticism about the literal truth of the Bible is an unwillingness to recognize their servitude, or the fact that being on balance a 'good' person is not enough.
Before we can know our Lord Jesus Christ as our saviour we need to repent of our sin  -  that is our sin, not our specific sins. We are not called to wrack our brains in egotistical contemplation before we are allowed into God's presence, but we must acknowledge that we are sinners, we must regret and repent our sin, we must mourn our sin.
John the Baptist was washing away the sins of his followers in preparation for the coming of the Lamb of God and his Kingdom of Heaven, when a people free from sin and superstition, receiving God's unending love, would receive grace for grace, and live fully eternally, in God's presence.