The body is the idea of sin. It is an extension of the idea of being separate. The body cannot become sinless in and of itself, although it can be used for a holy purpose.
"The body is the ego's idol; the belief in sin made flesh and then projected outward." - ACIM
"At no single instant does the body exist at all. It is always remembered or anticipated, but never experienced just now. Only its past and future make it seem real. Time controls it entirely, for sin is never present. " - ACIM
"Christ's vision has one law. It does not look upon a body, and mistake it for the Son whom God created. " - ACIM
The body is always a symbol of being separate from God. It must be imperfect and it must be an illusion. Otherwise, if it were not, it would be possible for the body to have power over the mind and could prevent the Son of God from awakening or healing.
The body itself, in its fullness, must be fundamentally an illusion of separation, and therefore sin. IT MUST BE FALSE. It can't be a truth and it can't have any truth to it. If truth were associated with the body, we'd be totally stuck in the dream.
To say that the body is inherently holy or perfect or anything other than a symbol of sin is to say that God, who is holiness and perfection, is a body. That is a way the ego wants to make God be a body so that it can kill God, just as it makes the Son of God a body in order to kill him.
"Any thought system that confuses God and the body must be insane." - ACIM
At its core, metaphysically, the body is an illusion of sin. It cannot be the central truth of who or what you are. It cannot be holiness. It cannot be wholeness. It cannot be innocence. It can only exist inside of the dream of separation. It cannot enter heaven. It is never present. And it never really exists at all.
We need to learn to recognize that the body is the idea of sin, and then undo it. If we are to undo sin, the body must disappear, being an illusion that we believe is really there as a real sin. You can perceive the body with love or use it with love to give it a holier purpose, in which it can appear to be free from sickness and so on, but it is still a body. It is still an idea and representation of sin, and so long as it remains, the mind cannot be 100% free. This is why Jesus had to disappear his body in order to completely remove its blockage to the awareness of God's presence.
The body is never present. It cannot exist in the now. It does not live. It is always a memory or an idea of the future, with an artificial history and a fabricated illusion of continuation. The body IS the symbol of sin. It is false. It does not exist. It not who or what you are. You do not need it. You are immortal spirit.
"Miracles reawaken the awareness that the spirit, not the body, is the altar of truth. This is the recognition that leads to the healing power of the miracle." - ACIM