Quote from A Course in Miracles Text Chapter 8 - THE JOURNEY BACK.

T-8.VIII.3. It has been particularly difficult to overcome the ego's belief in the body as an end, because it is synonymous with the belief in attack as an end. 2 The ego has a profound investment in sickness. 3 If you are sick, how can you object to the ego's firm belief that you are not invulnerable? 4 This is an appealing argument from the ego's point of view, because it obscures the obvious attack that underlies the sickness. 5 If you recognized this and also decided against attack, you could not give this false witness to the ego's stand.