“The next day he saw Jesus coming toward him, and said, “Behold, the Lamb of God, who takes away the sin of the world! 30 This is he of whom I said, ‘After me comes a man who ranks before me, because he was before me.’ 31 I myself did not know him, but for this purpose I came baptizing with water, that he might be revealed to Israel.” 32 And John bore witness: “I saw the Spirit descend from heaven like a dove, and it remained on him. 33 I myself did not know him, but he who sent me to baptize with water said to me, ‘He on whom you see the Spirit descend and remain, this is he who baptizes with the Holy Spirit.’ 34 And I have seen and have borne witness that this is the Son of God.” (John 1:29-34)
It seems John started out as a disciple of John the Baptist. He gives us more information concerning John the Baptist and what he preached than the other disciples. The Baptist tells his disciples that this is the man he had been preaching about, the one who comes after him but ranks before him because he was before him. This is the one he hails as the Lamb of God who takes away the sin of the world.
Here John the Baptist lets everyone know what is going to happen. Jesus will die. He will be a sacrifice for the world, the paschal lamb to be offered on our behalf. The one who ranks before the Baptist because he comes before him, the one on whom the Spirit descended, whose way was paved with a baptism of water, this man will die for our sins. He is the lamb of God who takes away the sins of the world.