“I tell you, among those born of women no one is greater than John;”

From a human perspective John was the greatest man that had been born (“among those born of women”).  He was greater than all the prophets that had preceded him.

“yet the least in the kingdom of God is greater than he.”

That is, with the coming of Christ, those born “of water and the spirit” into Christ’s death and resurrection are greater, even, than John the Baptist; entirely through their participation in Christ’s passion which has made them “a new creation.”