"Separation" is an ACIM buzzword and yet often misunderstood. Most people associate separation with something unnatural, something to remove, and a sign of the ego. Separation is bad, oneness is good. Anything that even hints at a sign of separation is considered to be wrong, some kind of "duality" which is opposite to the truth. But this is actually incorrect in ACIM terms.
If you look deeply at the course you may eventually realize that heaven's reality is not the same as the world of space and time. Heaven entails the sharing of everything. Spacetime entails NOT sharing anything. As you look deeper, you discover that God in fact isn't "arranged" like objects in spacetime. His whole mind and system and creation are in fact more like a holgoram.
"The recognition of the part as whole, and of the whole in every part, is PERFECTLY natural. For it is the way GOD thinks, and what is natural to Him, IS natural to you." The holographic principle is that there is a whole, and there are also parts. But each part isn't merely "a part of" the whole, lacking in some way. Each part in fact contains ALL of the whole. Every part is whole in and of itself, and is host to the whole. ACIM refers to this for example as "I am forever host to God." And "You had everything when you were created just as everyone did."
Each of the parts of a hologram experiences immense SHARING with the whole. And the whole includes all of God, and all other parts. This means that every part IS every other part, and is also host to God. This sharing, however, is not like sharing in spacetime. It does not mean that there are two separate things and something is transferred between them. Each part "houses" the whole, and therefore IS the same whole as the other parts. One part IS another part.
ACIM again expresses this in statements such as: "One brother is all brothers. Every mind contains all minds, for every mind is one. Such is the truth." This is not easy to understand in linear terms or by drawing analogies to spacetime objects, because in spacetime each object is "apart" from others, is NOT a whole, does NOT share anything, and is "separated off". This is not what it's like in a hologram. In the hologram, that which is in one part is located in all the other parts as well. It TRANSCENDS space and time, beyond spatial separations.
This also parallels very closely the idea of omnipresence, which is an attribute of God and everything he created. This doesn't just mean God is everywhere, it also means that THE WHOLE of God is in EVERY location. Not just one part of him over here, and another part of him over there. But ALL of him is simultaneously in multiple places. This again transcends the limits of space and time.
Now, in ACIM terms, the main whole is referred to as God, and the "whole parts" are referred to as souls, or God's children. There are a great many creations, which are many thoughts of God. Each thought of God IS whole, because God can only think wholly and in terms of wholeness. What he thinks of "creates another whole", which SHARES everything with the original whole and with all other wholes. Each whole is FUSED to all the others and effectively IS them.
This is the real meaning of oneness - a shared experience in which EACH wholly existing distinct "part" is united with and sharing everything with all the others. "The soul has not only been created perfect, it has been fully created." This is part of the miraculous nature of God, that a part of God is the whole of God, a creation of God contains all of God, and therefore every part "is one", and yet there are parts. These parts are not PARTIAL parts, or lacking what other parts have. Every part is A WHOLE.
Then we come to the idea of "the separation from God". This is where paople start to demonize the idea of separation or of "many things". When people don't recognize that heaven's natural state is one of TOTAL SHARING AND UNION, they may think of it more in terms of space-time objects. Such as the son of God is one "object". And then the only way to conceive of separation is to "split the object" so that there are now two or more objects. But this is NOT what happened in the separation, because heaven is not object-oriented or spatially separated.
In the separation, or "the fall of man", basically some of the WHOLE PARTS which were aspects of the hologram of God's thought, chose to STOP SHARING EVERYTHING. They wanted to become selfish. Their innate nature is to share everything with everyone. Everyone in heaven has everything. Everything belongs to everyone. Everyone IS everyone. "We are the Kingdom, WE, the sons of God." But "the ego" is actually the idea of trying NOT to share. And "the separation from God" was actually moreso an act of OPPOSING God's holographic family unit.
"The ego is the idea of selfishness. The soul is the idea of self-fullness."
The separation from God was a movement AWAY from sharing, towards selfishness. Selfishness goes by many names, all of which are efforts to "separate off", to withdraw, to hoard, and to move into a small isolated part which is NOT SHARED with the rest. This results in SPECIALNESS, which is the desire to have an exclusive special "something" true for you, which is not true for others.
Another way to view the separation is to say, individual whole parts of the hologram, rejected their union and shared totality with the whole, and tried to become "parts which do not share". They tried to orphan themselves. They did not want to be "part of" the collective sonship. They did not want to have the total holy relationship of sharing everything with everyone. They wanted to go of by themselves and have something special and exclusive just for them. "You were at peace until you asked for special favor, and God did not give it."
It's important to note then, that in fact in the creation of God, in the hologram of the Kingdom, there were in fact MANY INDIVIDUAL BEINGS prior to "the separation." God had created the sonship which comprised many souls, who are permanently brothers, and who were joined and sharing everything happily. These were INDIVIDUALS, but at the same time each individual was ONE WITH all the other individuals. Each one, is one and many, because the truth of a holographic system is that the one is many and the many are one.
The existence of many individual beings DID NOT MEAN that there were many "separate people" standing around like disconencted objects sharing nothing. That is not what multitudes are like in heaven. In heaven, many beings are individually present, AND YET at the same time, they are so intimately joined to and ONE WITH all other beings, that they ALL ARE one thing at the same time.
The separation from God did not actually INVENT "many selves". Many selves existed before that, and is completely natural. Nor did the separation produce individuality. But it DID produce a SECOND SELF, which was the idea of being not yourself and unlike how God created you - the ego. The denial of your joined identity (in christ - every soul is christ), formed a false self image.
"God who encompasses all being, nevertheless created separate beings (who SHARE, not who are isolated), who have everything individually and want **to share** it to increase their joy." "Nothing real can be increased except by sharing."
God had already created "many beings", not separate OBJECTS, or isolated cut-off individuals, but individuals who were ALSO joined together. They wanted to SHARE everything with each other, even their own souls. One soul IS another soul. There are many souls and each of them is an individual being, but also IS the other beings. The possibility of this is the "miraculousness" of the soul. You can see Jesus contrasting the WRONG way of thinking about the soul, here:
"Each Soul knows God completely (is the whole). This IS the miraculous power of the Soul (that it can be both a self and the whole at the same time). The fact that ***each Soul has this power*** completely is a fact that is entirely alien to human thinking, in which if any ONE has everything, there is nothing LEFT."
Indeed when we think in terms of spatially separated objects, we would conclude that if I have everything or am the whole, there is nothing ELSE for another soul to have. But in heaven, EACH individual being IS THE WHOLE. YOU are the whole sonship. "The Kingdom of Heaven IS you." I am the whole sonship. So are you. And WE are both there as brothers. Each PART of the sonship is the whole sonship. All the many children of God, which will always be many children of God and equal brothers, are the whole of heaven.
So in "the separation" event, some of the whole parts of the hologram rejected their SHARED nature, and wanted to ISOLATE. They didn't want to be included, they wanted to exclude. Thus they used denial and unwillingness and attack to reject the hologram. They were ALREADY individual beings, that have a total relationship of sharing with all others. But they tried to CUT OFF COMMUNICATION to end their shared relationships.
This turned them INTO "the separated ones." They BECAME separated, precicely because they existed in a NOT separated state before that. But this does NOT mean they didn't have an individual self before this. The only thing that changed was the loss of sharing (aka communication).
"Everything the ego perceives is a separate whole, without the relationships that imply BEING. The ego is thus AGAINST communication, except in so far as it is utilized to ESTABLISH separateness, rather than to abolish it."
"The separation was not a loss of perfection, but a failure in COMMUNICATION."
Some of the beings, who existed as whole beings, who had everything, who shared and WERE everything, "cut themselves off" from sharing anything, and isolated themselves. They wanted to have something SPECIAL for themselves. They tried to end their RELATIONSHIP with God. They wanted God to treat them with special favor. They wanted to be different and have something of their own. They wanted to be SELFISH.
Selfishenss is the opposite of sharing. Separation means a desire to be exclusive and selfish and to NOT SHARE. Which is why JOINING is its correction. And joining does not mean undoing your SELF!
To "be separate" therefore really means to NOT JOIN, or to not share. Spacetime is very obviously a state of not sharing. Each object is separated off. One car does not share with another car. One thing does not exist in two places at onces. Two things are not one thing. You cannot be located in one place and another at the same time. No two objects can overlap, otherwise they'd destroy each other. Spacetime was an attack on the SHARING of the sonship, resulting in a realm in which everything is separated off and excluded.
The body arose from the idea that you wanted to be isolated from the collective. You wanted to have something exclusive to you which others did not have - your own body. You wanted to be different than everyone else and not like them - your own appearance. You wanted to have some small portion of heaven that you thought of as exclusively yours, locked up inside a fence, surrounded by a wall, to keep others out and to keep you in. And you wanted to inhabit this small area of existence as exclusively yours, so that ONLY YOU exist within it and everything else is outside. This is what the BODY is based on. It is a separation device. And within it you are lonely and isolated, unless you are willing to extend or join PAST it.
"The body is a fence the Son of God imagines he has built to separate parts of his Self (holographic shared self) from other parts (your brothers who ARE also you). It is within this fence he thinks he lives, to die as it decays and crumbles. For within this fence he thinks that he is safe from love (wholeness/sharing)."
The UNDOING of separation, the atonement, healing, does NOT therefore necessarily mean ... ."let's get rid of anything that hints at separation". God had already created "separate beings" in heaven before the ego came along. They were separate in the sense that they were MANY, but they were ALSO JOINED. That which is BOTH many and one, is heaven's natural holographic condition. This is NATURAL. There is nothing wrong with it. It's perfectly legitimate that God has a family of souls. This has nothing to do with the ego.
"Ultimately, every member of the family of God must return."
Heaven means separate beings who are not separate. Whole parts which are parts but also the whole. There is an aspect of separation to that, because there ARE many beings. But they are not ISOLATED because they share everything. So the "attack on separateness" is NOT correct. The attempt to remove all sense of "separation" in all cases is NOT correct. We are not supposed to be removing the holographic aspects of reality. We are not supposed to be undoing the sonship. And we are NOT supposed to be getting rid of individuality!! You and your brothers all have permanent souls, created by God, which can never be destroyed.
What we ARE supposed to be doing, is realizing that we threw away what CONNECTS us. We threw away joining and sharing and RELATIONSHIP. We threw away holographic wholeness. We want to undo isolation, specialness, selfishness, possessiveness, ownership, exclusivity, localization, littleness, unwillingness to share etc. These are what being "separated off" really means. But we are not supposed to take it to the point of erasing ALL hints of "many things". God having many children is NOT a dualistic idea, because all of those many things ARE ONE as well.
Duality really means that there are many things which DO NOT SHARE. This is a false experience and is the basis for spacetime.
Nonduality is the idea that there are NOT many things. This is an attack upon heaven's creation and an attempt to claim that God is NOT holographic. It is ignorant and false and an ego conclusion.
Reality is in fact a kind of "trans-duality", a hologram, a paralogical and omnipresent system, in which many parts DO exist but they are NOT "separated off" parts like in spacetime. It is NOT duality to say that God has many sons, because while there are a count of many, they ALSO are fused together as one. They are WHOLE beings, who are each ALL the whole. And therefore each child of God is ALL children. This is why the sonship itself is united via the ONE MIND of christ, yet EACH INDIVIDUALLY is christ.
So we have to be careful when dealing with "undoing the separation" that we're not mistaken in trying to also undo the holographic aspects of creation. We can't just remove ALL trace of separation, because this undoes God's Kingdom. We can't just use a blanket statement to wipe out all notion of separateness because this kills off all the souls that God created. Separateness is therefore not really the PROBLEM. The problem is that the separate individuals are being selfish and don't want to SHARE THEMSELVES. It is a breakdown in communication and relationship that needs fixing, NOT individuality.
"Heaven includes all God's children and their creations." We can't just say "separation is a bad thing". It depends on whether or not the separate things are including or excluding each other. INCLUSIVE SEPARATION is perfectly normal. EXCLUSIVE SEPARATION is ego. The undoing of the ego is NOT the undoing of separation. It is the reversal of EXCLUDING OTHERS. This does not result in the erasing of individuality, nor of the undoing of multiple individuals. It results in a REUNION OF BROTHERHOOD in the sonship of God, in which all God's children are one big happy family who share everything with each other forever.