I was just reading in the Text last night, Jesus was talking about power. He said knowledge is power, and here he is talking about real knowledge - knowing, direct experience of truth/God, which occurs in Spirit. He spoke of how we still have the power of God but we've denied it and covered it up with all of the things we've taught ourselves (of the ego).
And in that context alone, He goes on to explain that we need to admit that the things we have taught ourselves are not really knowledge - they are things of the ego, and in that sense what we think we know is not really knowing... and so what we think we know, we don't actually KNOW, we just justify and rationalize that it's truth.
We need to let go of THAT.... but, we're only letting go of that ego education so that we can reveal to ourselves the power of God/true knowledge, which we DO know and can know. We need to get back in touch with the power of God (knowledge), and we need to become aware of what we really DO know. It's still in us, just hidden by false knowledge.
The things I think I know, I do not really know, and are not really knowledge. I need to let those go and not depend on them. Then I can become aware again of the presence of real knowledge with God (awareness of love's presence).