"You are not sick and you cannot die. But you can confuse yourself with things that do." - ACIM
Who we are is an immortal being. Period. That's all that we are. Immortal and safe and eternal and invulnerable and incapable of being sick or suffering or dying whatsoever.
But we CONFUSE ourselves with things that do seem to suffer and die. We confuse ourselves with a body, with an imaginary world, and with all kinds of fictional things.
Even if it seems the body is sick, you are not the body. But you are producing a sick body which indicates you don't quite believe you are not a body.
See, the body only shows up at all if your mind believes it is "made of" an illusion. It therefore expresses its idea of "self" and it shows up. If the mind believes it is a separate ego thing, a body appears. The more it believes this, the more the body that shows up appears to be sick. When it really binds its idea of self to "body", a dead body shows up.
But even a dead body cannot show up at all without a mind to make a dead body show up. Even if the body is lying there on the ground "dead", there MUST be a mind which is putting that body there, still.
This is the distinction that you are NOT the body and are not that which dies.
But this does not mean that it's therefore okay for the body to die. If the body dies it proves that you must believe in death, because you will ONLY create in like kind according to your beliefs.
Those who believe in immortality only create that which is immortal. Those who believe in death create bodies which appear to die.
And having believed death is real, we will make bodies which appear to be dead as though real, because that's what we believe is truth. Believe it and you will create it.
There are some who believe that in the atonement sick bodies and healthy bodies are all the same illusion - which is true - and that therefor (this is level confusion), when you are in the world it does not matter if your body is sick or not.
It does matter.
The body cannot be sick without the mind being sick.
The body cannot seem to die unless the mind believes in death and victimhood.
A sick/broken/dead body is PROOF the mind has NOT been healed.
A slight belief that you are a body, manifests a slightly sick body.
A stronger belief that you are a body manifests a suffering body.
A really extreme belief that you are a body, produces a dead body.
See how the ego always produces the exact opposite of what it says it is going to do. Believing you are a body should surely produce an everlasting body, right? Wrong. It does the opposite.
Believe you are a body and you will NOT succeed in being a body, you'll produce a dead one.
ie it is literally impossible to be a body, for real.