The body is a separation device. It was made to section off and fence in a SMALL PORTION of mind, which seems then to find itself housed "inside" the body, while the larger portion of mind appears to be "separated off" or unconscious, outside the body. The sense of being isolated, separated, limited, partial, not whole, thus belongs to the "inside the body" experience, which is an experience of being only PART of yourself. To return to wholeness you have to thus transcend the body, erase the body, have no separation devices in the mind, and therefore collapse the gap between the outer and inner. The body symbolizes the split in the mind and once the split is erased the body is erased.
"God cannot come into a body, nor can you join Him there. Limits on love will ALWAYS seem to shut Him out, and to keep you APART from Him. The body is a tiny fence around a little part of a glorious and completely limitless idea. It draws a circle, infinitely small, around a very little segment of Heaven, splintered from the whole, proclaiming that, within it, is YOUR Kingdom, where God can enter not. Within this kingdom the ego rules, and cruelly. And, to defend this little speck of dust, it bids you fight against the universe."
Since the body itself is a separation device BETWEEN parts of mind, designed to keep one part of mind sectioned off from the other part, it can only seem to EXIST at all while there is a sense of separation. If the mind is split, the split shows up as a body coming between "you" (within the body) and the rest of you (outside the body, in others). The body is thus a symbol of separation in the mind, and when the mind does not have separation in it there cannot be a body at all.
This is why God cannot enter a body, because that's like saying you can keep a separation device, something which sections off inner and outer, and keeps them apart. It's like saying the whole of God which is everywhere (within and without) can be stuffed inside a container which is less than everywhere, and all of God can thus be housed inside a box and be ABSENT from the outside. This is utterly impossible because God is unlimited and infinite and all encompassing.
Thus God, all of God, cannot enter a body or dwell in a body entirely. Nor can you, who find yourself to "be in a body" or rather, who have a split mind which shows up AS a body coming between you and the rest of you, join with God fully while maintaining a body. The body can only be there IF there is separation in the mind. If the mind has NO belief in separation it utterly not only transcends the body but ERASES the body. There can be no body at all without a belief in separation. Total wholeness wipes the body away completely. Meaning that to truly be whole you cannot be inside a body. And you therefore cannot fully MEET, join, be one with all of God, while there is a body present. You have to leave the realm of bodies entirely to be infinite and unlimited.
"Forgiveness is an earthly form of love, which as it is in Heaven has no form. Yet what is needed here is given here as it is needed. In this form you can fulfill your function even here, although ***what love will mean to you when formlessness has been restored to you is greater still.***"
This is similarly why you cannot be Christ in a body, IMO. Christ is similarly unlimited and whole and infinite. Just as is your soul. Your soul cannot enter a body either. "The body neither lives nor dies because it cannot contain you who are life." Christ cannot directly in a first-person way be CONFINED in a body or sectioned off and found to be isolated to one place and not another. However, I believe ACIM is saying that you can "channel" Christ in a body, to some extent. You can be close to Christ and you can extend His love and miracles, but it's like he is working "through you" once removed, not directly.
I don't think Jesus was thus "Christ in a body" because if Christ could be in a body, fully, with no limitation at all, bodies could coexist with Christ and be his equal, and bodies would then have to exist in heaven as creations. Christ is unlimited, infinite, everywhere, and bigger than the universe. In ACIM Jesus lets us know that he "was a man who remembered his soul" and he remembered it in the atonement and ascension to heaven. And prior to that, he still had some trials and lessons, not least of which was the crucifixion. He BECAME identified fully with Christ, but not until getting out of here.
"To roll the stone away is to see beyond the tomb, beyond death, and to understand the body’s nothingness. What is understood as nothing must disappear."
"The death of an illusion means nothing. It disappears when you awaken and decide to dream no more."
"My body disappeared because I had no illusion about it. The last one had gone. It was laid in the tomb, but there was nothing left to bury. It did not disintegrate because the unreal cannot die. It merely became what it always was."