The leaders should have listened to John. He was “a prophet … more than that” (Matthew 11:9-11). Yet, as great as John was, the Coming One would be much greater. John himself said,
“I baptize you with water for repentance, but he who is coming after me is mightier than I, whose sandals [shoes] I am not worthy to carry. He will baptize you with the Holy Spirit and fire.“ (Matthew 3:11).
John could hardly touch the shoes of the Coming One. John used water for baptism; the Coming One could do something far greater – He would baptize using God’s Spirit! The Holy Spirit is a part of God Himself. Who would be so great that He could use the Holy Spirit as John used water?
Yet this Coming One looked like an ordinary man. So John, by himself, had no way to recognize Him. God told John to look for this sign: The Holy Spirit would take the shape of a dove and come down on the Coming One.