Quote from ACIM Text Chapter 7, Section 2 - The Law of the Kingdom.

To heal is the only kind of thinking in this world that resembles the Thought of God, and because of the elements they share, can transfer easily to it. When a brother perceives himself as sick, he is perceiving himself as not whole, and therefore in need. If you, too, see him this way, you are seeing him as if he were absent from the Kingdom or separated from it, thus making the Kingdom itself obscure to both of you. Sickness and separation are not of God, but the Kingdom is. If you obscure the Kingdom, you are perceiving what is not of God.