Jesus delivers this unfamiliar irksome preaching right at his hometown, Nazareth. Imagine what would happen next. His hometown people get angry and attempt to hurl him off the cliff. Then Jesus says no prophet is accepted in his hometown. I can imagine what Jesus would have to say to them: "Because they know too much about me!" In other words, because they think they know everything about Jesus, they don't see beyond what they know, or they don't know beyond what they see. They know him too well from their perspective: about his rural background, about his poor parents, about his youth days, and so forth.
Because they think they know well about Jesus, they don't even try to understand what Jesus reads or says. Jesus emphasizes God's equally special love for the other marginalized people outside of the Jewish territory because God is impartial! As heaven is impartial, God is impartial. God is great because of God's impartial love. That is the point of a lesson.
But people at his hometown miss this point of teaching because of their seemingly confident knowledge about Jesus and their special place in God's love. One's special place or sense of love cannot deny God's love for others. From God's perspective, everyone is special, every tribe is special, and every race is special. One's special place cannot relegate others to lesser humans. That is what we believe God's impartial love means. See what Jesus says about God's impartial love in Matthew's Gospel: "so that you may be children of your Father in heaven; for he makes his sun rise on the evil and on the good, and sends rain on the righteous and on the unrighteous" (Matthew 5:45). We often forget this simple truth.
We are also reminded by the story of a blind man in chapter 9 of John's Gospel. The Pharisees say, "Only we are disciples of Moses." In their eyes, all who work outside of the traditional Jewish school must not be from God. Ironically, their confident knowledge about God prevents them from seeing Jesus' work of God.
It is not uncommon to find a sort of wisdom stated above from other sages in ancient worlds. Lao-tzu, a great deconstructionist philosopher, in 5-6th century BCE China, says, "Know that you do not know; that is the best" (from the TAO TE CHING). Similarly, Socrates says, "All I know is that I do not know." Wow!