When your sense of identity has become confused with the ego or body, you see it as your SELF. You associate your existence with it as though it is you.
In order to then preserve your "own life", you will defend the thing you are identified with because you think it is really you. When it is threatened, you are threatened. You will therefore seek to maintain and preserve IT at all costs.
When the truth comes along to reveal that you are not the ego or body, your ego-identified self WILL perceive it as a threat. It’s a threat because IF the truth is true, it proves that the ego is not real. If YOU are the ego, that means YOU are not true and you don’t really exist.
What could seem more threatening than this implication that "you are going to be undone", or "your life" is going to end because what you ARE is being attacked by the truth?
In the name of protecting what you THINK is your life - your self, you will DEFEND your "self". Or at least, you think you are. You are defending the ego because you think it is your self, not recognizing it as not you, because you don’t recognize who you really are.
To defend yourself AS the ego, you will USE ego methods to protect yourself. The ego has only one tool - separation, which is the same thing as denial. In the name of what you THINK is protecting your SELF, you will implement MORE separation to try to put safe distance between you and the truth.
When you emphasize more separation, you split your mind, increase mental illness, and foster sickness in the body. This is unavoidable. Choosing to withdraw from truth is choosing to withdraw from life and health and wholeness. The defense that SEEMS like it is there to PROTECT you and save your life, with the purpose of self-preservation, is actually HURTING you. It makes you sick.
The ego is insane and every guidance it gives is a lie that does exactly the opposite to what it claims. It claimed that you protecting it (you) would make you safe from attack. Instead, it attacked you and now you are sick and worse off. The signs and symptoms of sickness start to show up in the body as well. You tried to protect yourself and you were attacked ("if I defend myself I am attacked").
In this state, you are WILLING TO TOLERATE SICKNESS and KEEP IT because, to your ego-body-identified self, the purpose of the sickness is to KEEP YOU SAFE. While you perceive that you NEED this defense, to keep your "self" safe from the truth, you will NOT be willing to drop the sickness. To do so would make you LESS safe and expose you to the perceived attacker. No-one in their right mind would want to become more vulnerable to attack, so it seems a reasonable to maintain and increase the sickness.
Even though the sickness is intolerable, and suffering is awful, you unconsciously chose it on purpose. Consciously now, because you are in denial and implemented denial in order to make the threat go away, you have blocked awareness of the choice you made.
You therefore don’t see that you did it to yourself. You then will see the symptoms of sickness as unchosen, unwanted, undesired and unacceptable. You will seek externally for possible "causes" trying to explain what caused the sickness to show up. It was you.
The secret to salvation is that you did this to yourself. The sickness is protecting you from God. The more you can make the body sick, the more pain it is in, the more you will focus on the body. You withdraw and contract yourself towards it, hugging it tightly in pain, because doing so reinforces your sense that you ARE the ego body. The more identified with the body you are, the more you are trying to make your ego-self strong. The more tightly you cling to it, the sicker it becomes.
The body is the primary place where you escape from God’s wrath, and yet escaping to it attacks it. An increase in confinement and isolation and body-identification seems to prevent God from stealing your identity away - your self, which you are trying to protect. But the more you BIND yourself to the body in suffering, the sicker you become. You simultaneously believe you are actually becoming SAFER from God, but are horrified that you also are in a state of suffering. The sickness seems to prove that the truth is attacking you, and that you do not want it.
The ONLY problem here is a mistaken sense of identity. If we did not believe we are the ego or the body, we would not perceive our SELF as under threat from the truth. We would have no reason to defend ourselves because we would be strong and truly safe. And recognizing ourselves as immortal we transcend the NEED for sickness. Without a purpose of protection, sickness HAS no purpose, and not perceiving a purpose in it, you will withdraw your belief in it. "Illusions recognized must disappear". Sickness will vanish.
Atonement cures because it removes the perceived NEED for the sickness. Accepting atonement is a willing acceptance of the truth without resistance or fear. In that willingness there is no more identification with ego or body. Nothing to defend, nothing under attack, nothing real can be threatened. In this is the TRUE escape from all sickness and death forever. Atonement is the resurrection of God’s Son to eternal life.