To prove that your mind is restored to sanity and to its truly immortal nature, you must also be willing to prove physically that you are invulnerable. This demonstration of invulnerability requires great confidence, in that even when others attempt to harm you, the consequences of their attack disappears and is undone. You become "bullet proof" and incapable of being hurt by anyone.
You are literally being asked to show your brother, to prove to him visually, that on ALL levels, you have not been hurt by him. This includes and demands the healing of the body, so that it does not transmit a double contradictory message. The body must not be allowed to testify that HE DID attack you or your body, otherwise it continues to PROVE that he is a sinner.
This requires the use of miracles to override all external sources of attack, undoing all consequences of sin, and maintaining the body in perfect condition. Only by reversing or preventing any effects of attack by another, can you truly demonstrate to him that he HAS NOT attacked you OR your body. And only by showing him the complete ABSENCE of evidence to support his belief that he sinned, can you exonerate him and teach him his innocence.
Your body then becomes a SYMBOL of your own innocence, because it now represents your harmlessness and immortality. And by pointing TO your innocence, it also testifies to HIS. It cannot testify to his innocence if it retains ANY trace of harm or damage, which means that until forgiveness has brought a PHYSICAL healing to your body, it is not real or complete. And until it has transmitted healing TO your brother as well, through physical demonstration, forgiveness is not complete.
When you brother attempts to look upon your body which he believes he DID successfully attack, and does NOT see any proof of attack there, because it has been healed and undone by miracles, it becomes impossible for him to CONFIRM his own sinfulness. And in the demonstrated PHYSICAL PROOF that he did not do anything, the body testifies with a power greater than a thousand tongues, and beyond words or claims, that HE MUST NOT have attacked you. And therefore your body's unharmed condition shows him that he MUST still be innocent, and in its harmlessness induces HEALING in him, because his belief in sin is proven false.
This also extends to you demonstrating that your brother has not hurt you psychologically, and is not responsible for your suffering. Which ties into the secret of salvation that "you can be hurt by nothing but your thoughts" and "you did it to yourself." When someone appears to upset you, you are deceiving yourself and are using him as a scapegoat for your self-attack.
What you're supposed to do is assert that NO ONE CAN HURT YOU. Which is a position is great confidence and assertion. Whereby even if someone tries to hurt you, you act as if they have had NO EFFECT on you. Which means you do not hold anything against them.
To forgive therefore means to hold no sense of sin or guilt against anyone, REGARDLESS of what they do or attempt to do. Even if they accuse you or try to hurt you, you stand in the face of their onslaught unharmed and unwavering, like a rock in the river. You do not USE it to hurt YOURSELF, and so do not demonstrate that you can BE attacked. You show your brother, both mentally and physically, that he HAS NOT done anything to you, and you do not make him responsible for your condition, feelings, or physical state. You act as if you are invulnerable, and in fact are. You show him, "you can't do anything to me, not even physically."
If you think ACIM is not teaching you that you HAVE to heal the body in order NOT to accuse others of sin, then think again. The body MUST reflect the healed mind, and until it does, you HAVE NOT healed the mind. Sickness and pain cannot be kept, if you are to PROVE that you are healed and that you have power OVER it. Death and sickness must be UNDONE in order to demonstrate that you are the resurrection and the life.
This doesn't mean you ARE a body OR that the body is immortal, which it cannot be. But the body DOES symbolize your mind, as an outward picture of an inward condition. Its sickness is part of your effort to PROJECT SIN, and you cannot allow it to show up as a picture of crucifixion or proof of attack, if you are truly forgiving.
The pertinent quotes...
"The power of witness is beyond belief, because it brings conviction in its wake. The witness is believed BECAUSE he points beyond himself, to what he REPRESENTS. A sick and suffering you but represents your brother's guilt; the witness which you send, lest he forget the injuries he gave, from which you swear he never will escape. This sick and sorry picture YOU accept, if only it can serve to punish him. The sick are merciless to everyone, and in contagion do they seek to kill. Death seems an easy price, if they can say, "Behold me, brother, at your hand I die." For sickness is the witness to his guilt, and death would prove his errors MUST be sins."
"To witness sin, and yet forgive it, is a paradox which reason cannot see. For it maintains what has been done to you DESERVES no pardon. And, by GIVING it, you grant your brother mercy, but retain the proof he is not REALLY innocent. The sick remain accusers. They cannot forgive their brothers AND themselves as well. For no-one in whom true forgiveness reigns CAN suffer. He holds not the proof of sin, before his brother's eyes. And thus he MUST have overlooked it, and removed it from his own."
"Health is the witness unto health. As long as it is unattested, it remains without conviction. Only when DEMONSTRATED has it BEEN proved, and MUST compel belief. No-one is healed through double messages. If you wish ONLY to be healed, you heal. Your single PURPOSE makes this possible."
"What you would prove to him you will believe. The power of witness COMES from your belief. And everything you say or do or think but testifies to what you teach to him. Your body can be means to teach that it has never suffered pain because of him. And in its healing can it offer him mute testimony to his innocence. It is THIS testimony that can speak with power greater than a thousand tongues. For here is his forgiveness PROVED to him. A miracle can offer nothing LESS to him than it has given unto you. So does your healing show your mind is healed, and has forgiven what he did NOT do. And so is HE convinced his innocence was never lost, and healed along with you."
"Forgiveness is not real UNLESS it brings a healing to your brother AND yourself. YOU must attest his sins had no effect on YOU, to demonstrate they were not real. How else COULD he be guiltless? And how COULD his innocence be justified UNLESS his sins have no effect to WARRANT guilt? Sins are beyond forgiveness just BECAUSE they would entail effects which CANNOT be undone and overlooked entirely. In their UNDOING lies the proof that they were merely errors. LET yourself be healed, that you may be forgiving, offering salvation to your brother AND yourself. A broken body shows the mind has NOT been healed. A miracle of healing proves that separation is WITHOUT effect."
"Thus does the miracle undo all things the world attests can never BE undone. And hopelessness and death MUST disappear before the ancient clarion call of life. This call has power FAR beyond the weak and miserable cry of death and guilt. The ancient Calling of the Father to His Son, and of the Son unto his own, will yet be the last trumpet that the world will ever hear. Brother, there is no death. And this you learn when you but wish to show your brother that you had no hurt of him. He thinks your blood is on his hands, and so he stands condemned. But it is given you to SHOW him, by your healing, that his guilt is but the fabric of a senseless dream."
"The body can become a sign of life, a promise of redemption, and a breath of immortality to those grown sick of breathing in the fetid scent of death. Let it have healing as its PURPOSE. Then will it send forth the message it received, and by its health and loveliness proclaim the truth and value that it represents. Let it receive the power to represent an endless life, forever unattacked. And to your brother let its message be, "Behold me, brother, at your hand I live."
"Now in the hands made gentle by His touch, the Holy Spirit lays a picture of a DIFFERENT you. It is a picture of a body still, for what you REALLY are can not be seen nor pictured. But THIS one has NOT been used for purpose of attack, and therefore never suffered pain at all. IT witnesses to the eternal truth that you can not BE hurt, and points BEYOND itself to both YOUR innocence and HIS.
Show THIS unto your brother, who will see that every scar is healed, and every tear is wiped away in laughter and in love. And he will look on his forgiveness there, and with healed eyes will look BEYOND it, to the innocence that he beholds in you. Here is the proof that he has NEVER sinned; that NOTHING that his madness bid him do was ever done, or ever had effects of any kind. That NO reproach he laid upon his heart was EVER justified, and NO attack can touch him with the poisoned sting of fear. Attest his innocence and NOT his guilt. YOUR healing is his comfort and HIS health. BECAUSE it proves illusions were not true."
The central lesson is always this; that what you use the body for, it will become to you. Use it for sin or for attack, which is the same as sin, and you will see it as sinful. Because it is sinful it is weak, and being weak it suffers and it dies. Use it to bring the Word of God to those who have It not, and the body becomes holy. Because it is holy it cannot be sick, nor can it die. When its usefulness is done it is laid by, and that is all. The mind makes this decision, as it makes all decisions which are responsible for the body's condition. Yet the teacher of God does not make this decision alone. To do that would be to give the body another purpose from the one that keeps it holy. God's Voice will tell him when he has fulfilled his role, just as It tells him what his function is. He does not suffer either in going or remaining. Sickness is now impossible to him.
"The guiltless mind cannot suffer. Being sane, it heals the body because IT has been healed. The sane mind cannot conceive of illness, because it cannot conceive of attacking anything or anyone."
"His dreams are happy and his rest secure; his safety certain and his body healed"
"With THIS as purpose IS the body healed. It is NOT used to witness to the dream of separation and disease."
"Now is the body healed because the source of sickness has been opened to relief."
"Thus is the body healed by miracles BECAUSE they show the mind MADE sickness, and employed the body to be victim, or EFFECT, of what it made."
"That is why the Bible says "There is no death," and that is why I demonstrated that death does not exist."