Then John gave this testimony: "I saw the Spirit come down from heaven as a dove and remain on him. I would not have known him, except that the one who sent me to baptize with water told me, 'The man on whom you see the Spirit come down and remain is he who will baptize with the Holy Spirit.' I have seen and I testify that this is the Son of God."
John 1:32-34
God has always provided objective evidence to undergird our faith. I don't mean that every aspect of our faith has something tangible supporting it, but that God has provided enough of a foundation to justify those times when we must take that "blind leap of faith." Surely, there was much about Jesus that John did not understand. But he could confidently proclaim the parts of God's message he didn't understand, because God gave him clear evidence of the veracity of Jesus of Nazareth.