If it is true that we are still as God created us, and we are still immortal spirit, and nothing has happened, then if we were to fully express this truth in this world, we would show up in a "perfect" healthy form with no sign of corruption or decay or sickness.
Jesus asks that we do this, because if we are not showing up this way, we are demonstrating that we can be hurt, and so are accusing our brother and ourselves of sin.
So let's say that you have this `perfect self` which is SUPPOSED to be expressing and showing up here temporarily, to prove that Heaven is real and God's laws override the ego. So now, if that is not happening, if there is a problem showing up or a sickness or some kind of symptom, then we have attempted to ADD on top of our perfection, something artificial, and are now seeking outside of ourselves, and this is materializing as visible symptoms of decay and sickness and damage.
So now we need to reverse that, undo that, and allow our true light to shine. If our true light is not shining, then we have blocks to awareness. If form seems to demonstrate that we are not divinely healthy, then something is blocking awareness. It means we're trying to prove otherwise.
What you use the body for it becomes to you. If you use it to project attack then it is attacked and it becomes sick and shows up as physical sickness. If you use it to bring the word of God (the word being, the nature of God), to those who seem to have it not, the body is being used for extending love and so is restored to perfect health and demonstrates perfection
This "symbol of immortality" as Jesus puts it, proves that you cannot have been affected against your will, therefore your brother is innocent. And your immaculate body teaches him that he cannot have attacked you, since there are no effects.
Are you willing to bring forth a "living demonstration" that God's laws are true, and that you can be affected by nothing?