John was sent by God the Father to identify his Son Jesus as the Messiah to the nation of Israel and to show their need for a new way to attain salvation. And he used baptism to do it!
The religious leaders knew that the messiah was bringing salvation; they had read what the prophets had written years before. They just didn’t know how it was going to come about. So when they heard about John’s baptism, they confronted him about it. He responded to them saying that his baptism was only with water; the real thing was yet to come.
The next day he saw Jesus coming to him and said, “Behold, the Lamb of God who takes away the sin of the world! This is He on behalf of whom I said, ‘After me comes a Man who has a higher rank than I, for He existed before me.’
I did not recognize Him, but so that He might be manifested to Israel, I came baptizing in water.” (John 1:29-31)
John is known for preaching repentance. His message told of a new way to receive forgiveness. It was through faith in the “Lamb of God”; rather than the Law and its endless sacrifices. Repentance from sin was not about changing a person from being sinful to being sinless. Repentance is changing the way a person gets forgiven. It is changing from trusting in mans’ efforts to trusting in God’s provision through His Son.