I would not have known him, except that the one who sent me to baptise with water told me, ‘The man on whom you see the Spirit come down and remain is he who will baptise with the Holy Spirit.’
Again John states that he did not know the Messiah. He could have meant that he didn’t personally know Him, since John grew up in the deserts of Judea and Jesus grew up in Galilee, but more probably it means that John didn’t know who it was that he was going to baptize with the Holy Spirit until he received the sign God had promised. As Morris points out, “recognition came not from prior knowledge, but from supernatural revelation.” (NICNT p. 152) God does not usually give us full revelation of the things He has for us. He most often tells us just what we need to know.