@ninja8tyu like, the quote?
@ninja8tyu it is easier to understand if you look at it in context. In Matthew 17, Jesus is talking about false prophets. He warns of people who seem outwardly righteous but have ulterior motives. People are judged by their actions, aka their "fruits" in this example, not their word alone.
Jesus talks more about these types of people in Matthew 23. Everything these people do is working towards being seen as righteous to man, not for the Lord. They are disingenuous.
Jesus doesn't know them because they never truly knew Jesus. They claim they do because that is how they gain their worldly power, but their true works, their fruit, are poisoned.