John 1:29-34

(29)The next day he saw* Jesus coming to him and said*, “Behold, the Lamb of God who takes away the sin of the world!

Jesus came to us when He was born a human and accomplished our salvation on the cross. He comes to us at the moment of our salvation for it is He who seeks us not us who seek Him. Jesus also comes to us and is truly with us every second of every day in His Holy Spirit. Do we constantly “see” Him in our lives and acknowledge Him as the Lamb of God who takes away the sins of the world?

(30)“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.’

John continues to speak of Jesus’ deity in saying that “He existed before me.” John reiterates confirmation that Jesus is God at many times and in many ways throughout this book. Anyone who refutes the deity of Jesus Christ will have a very difficult time explaining the many passages John has given us through the inspiration of the Holy Spirit.

(31)“I did not recognize Him, but so that He might be manifested to Israel, I came baptizing in water.”
(32)John testified saying, “I have seen the Spirit descending as a dove out of heaven, and He remained upon Him.
(33)“I did not recognize Him, but He who sent me to baptize in water said to me, ‘He upon whom you see the Spirit descending and remaining upon Him, this is the One who baptizes in the Holy Spirit.’
(34)“I myself have seen, and have testified that this is the Son of God.”

John states here that he did not recognize the Lord prior to His baptism and the Holy Spirit descending upon Him as a dove. In Matthew 3:13-17, John is clear that he did recognize Jesus as the Lord before His baptism.

Matthew 3:13-17
(13) Then Jesus came from Galilee to the Jordan to John, to be baptized by him.
(14) John would have prevented him, saying, "I need to be baptized by you, and do you come to me?"
(15) But Jesus answered him, "Let it be so now, for thus it is fitting for us to fulfill all righteousness." Then he consented.
(16) And when Jesus was baptized, immediately he went up from the water, and behold, the heavens were opened to him, and he saw the Spirit of God descending like a dove and coming to rest on him;
(17) and behold, a voice from heaven said, "This is my beloved Son, with whom I am well pleased."

This is not a contradiction. John received his assignment from God, as we all do. He did not arbitrarily decide on an assignment himself. He was given the grace (spiritual gift) by God to recognize the messiah before he was even born. When Mary (pregnant with Jesus) came to visit her cousin Elizabeth (pregnant with John), John leapt within Elizabeth’s womb when he was in the presence of the unborn messiah. God gives confirmation of the authenticity of Jesus as messiah through John’s declaration.
John declares to his disciples, that it is not by his own testimony that they should believe Jesus is the Christ, but by the declaration of God Himself. God declared that Jesus is His son by having a dove descend upon Him at His baptism and by speaking the words “This is my beloved Son, in whom I am well pleased.” In the same way God gave John his assignment and the grace to perform it, He gives us all the ability, through our spiritual gifts, to perform the assignments He gives us.