Why did John the Baptist send his disciples to ask Jesus whether he was the one or for them to look for another? He is the same person who said “Behold the lamb of God who takes away the sins of the world.” So what is the Gospel of Matthew trying to tell us in this passage?
This is a great question. John the Baptist and some of his disciples had spent time with the Essenes who believed that there would be two Messiahs. They got this idea by looking at all the Messianic prophecies and noticing that some of them described a suffering servant and others described a conquering King. They called the servant Messiah ben Joseph, after Jacob’s son in Egypt, and the King Messiah ben David after Israel’s beloved King. (Ben means “son of” in Hebrew.)
John knew that he would soon be executed so he sent his disciples to Jesus with the question you refer to. He knew exactly who Jesus was, but he wanted to settle the confusion over the Essene’s view for them.
What he really sent them to ask was, “Are you the (only) one who was to come or will there be another (different from you)? This is much clearer in the Greek language than in the English so a lot of people miss it.
But the Lord’s answer confirmed that He was the only one, because He reminded them of the teaching and preaching He was doing that the Essenes attributed to Messiah ben Joseph (Isaiah 61:1), and the healing and raising the dead He was also doing that they attributed to Messiah ben David (Isaiah 35:5-6). By this He was saying that there weren’t two Messiahs, but one.