Mark 10:15 “Truly I tell you, anyone who will not receive the kingdom of God like a little child will never enter it.”
We have to re-learn how to see things. Our hearts our often hard (Mark 10:5). Our hands are often doing things they ought not (Mark 10:43). We have trained ourselves according to the patterns of this world. We need the Spirit to be our pedagogue to train us in all holiness so that we might grasp the Kingdom with new eyes. Or, we always enter into a posture of disection--critical analysis--thus keeping our eyes from witnessing the glory of in-breaking Kingdom. We need eyes that for the first time grasp the beauty of color, the phenomenon of the Kingdom.
All this, it would seem, is what Jesus is referring to--and certainly more.
This reference to receiving the Kingdom like a child is another way of explaining the new birth and the conversation Jesus has with Nicodemus. We must have our minds renewed so that we can grasp the Kingdom anew—the world has been, too much, our teacher.