“I did not know He was the One” (Messiah, the Great I AM, God of Israel) has been said by John the Baptist.
We read in, John 1:33;
“I didn't know He was the One, but when God sent me to baptize with water, He told me, “The One on Whom you see the Spirit descend and rest is the One Who will baptize with the Holy Spirit.””
John must have known who Jesus was (humanly speaking) as a relative of Jesus because Mary and his mother Elizabeth was a close relative.
We read in, Luke 1:35-37;
“The angel answered, “The Holy Spirit will come upon you, and the power of the Most High will overshadow you. So the Holy One to be born will be called the Son of God. Even Elizabeth your relative is going to have a child in her old age, and she who was said to be barren is in her sixth month. For nothing is impossible with God.””
How did John the Baptist know Jesus is the Son of God Who baptizes with the Holy Spirit?
God told him so.
He told me, “The One on Whom you see the Spirit descend and rest is the One Who will baptize with the Holy Spirit.””
Who told Peter Jesus is the Christ and the Son of the Living God? God the Holy Spirit told him so.
We read in Matthew 16:15-17;
“But what about you?” he asked. “Who do you say I am?”
Simon Peter answered, “You are the Christ, the Son of the living God.”
Jesus replied, “Blessed are you, Simon son of Jonah, for this was not revealed to you by man, but by my Father in heaven.””
As for any person who doesn’t know Who Christ really is, I think it is natural for human not to know of God by him or herself. Even the Apostle Paul said so;
“So then, from now on we do not think of anyone from a human point of view. Even if we did think of the Messiah from a human point of view, we don't think of Him that way anymore.”
When he met the Risen Lord on the way to Damascus, he changed and came to believe Jesus is the Lord God Whom he waited for.
Pray to God earnestly so you can believe Jesus is the Messiah, the Son of God. Then the Holy Spirit of God will descent on you and make you follow Jesus from here to eternity! Amen.