"Paul…someone asked this of me earlier and I gave my best answer, but thought I would love to hear yours. How do we understand and reconcile the concept of non-duality in ACIM while still appreciating the beautiful parts of life as we now live it (in separation)?"
First of all let's clarify the Course's non-duality. A Course in Miracles is a "pure" non-dualistic teaching. In general, non-duality teachings believe that "duality" - i.e. a world of opposites and differences, is not real or true. That in truth, there are no opposites or differences, there are not two sides or multiple personalities or opponents of any kind.
However, many non-duality teachings are not quite purely consistent and are not quite taken all the way to their logical conclusion. Therefore many non-dualistic teachings will say, everything in the world is "oneness", every object is joined, every person is connected, there really is a real world here which is showing up as though there are differences but really it's all one thing.
That's a great step forward, but it is not the whole truth taken to its logical conclusion. It is contradictory in that, it is claiming that oneness can coexist, in reality, at the same time as a world of differences. It also is suggesting that the world itself is somehow real and actually does exist, just that we need to realize it is secretly a oneness. This awareness, however, apparently does not undo the idea that the world exists at all, it merely sees it from a perspective of unity.
This kind of non-duality equates to what A Course in Miracles calls "True Perception", with which you are still perceiving a world, but you are recognizing that it is all the same world, a single experience with no conflict. This could also be equated to the Course's description of the "forgiven world", where you still see the world as though it exists, but do not see guilt or sin in it. You see it from a mind which seems to be whole, but the world is still seen.
This doesn't quite take it all the way. If you look at this, oneness and duality cannot coexist, and not even an illusion of differences can continue to seem to exist, if the mind is purely, completely, whole and healed and unified. Illusions are actually attempts to split the mind, and they exist only as "dreams" in the mind. If the mind becomes awakened to the fact that all of its illusions are false and unreal, then that awakening must lead to the DISAPPEARANCE of those illusions.
If you also look at the world, you will recognize that it is fundamentally based on an idea of separation. All particles are separate and all matter and objects are separate. It is a picture of the opposite of omnipresence. The opposite of God. The opposite of reality. It simply cannot coexist with reality. A mind which has reached True Perception will very quickly move on to Vision, which ACIM refers to as the ability to truly SEE and to know that there is ONLY Oneness.
This is also reflected in the Course's statement that nothing real can be threatened and nothing unreal exists. In this view, and as the central theme the course would aim to teach, there literally IS no world. It is not "really" a world of oneness, or a world without duality. It is NOT a world. It is not even really there. If the mind that is dreaming it would cease to believe in it, it would cease to MAKE it, and it would literally disappear.
In the Course's metaphysics, the ultimate truth is that there is only God. There is no world at all, either illusory or real. This is the only way that the idea of oneness can be logically consistent. If there is true, complete oneness, there is no way there can be a two-ness, or a multitude. There can be no illusions, there can be no separations, there can be no objects, there can be no forms of matter. It is completely abstract. Such is the mind of God. And in that truth, there is only light, there is no world at all.
So where the Course goes above and beyond most non-duality is that it is PURE, 100% logically consistent, far reaching and completely extreme in its metaphysics. It goes beyond even the idea that the world is "all one". It is claiming that there is no world whatsoever. That there is, in reality, only oneness and no illusions of worlds anywhere. This goes beyond non-duality to pure non-duality, and takes us beyond the entire physical universe.
Now. There is quite a big difference between what you can explain or understand on an intellectual level, and what you are experiencing. Your experience is more real and true to you than mere thoughts or information or discussion. If you are currently experiencing that you believe this physical world is real, as in, it actually does exist as part of Reality, then you are going to have a very hard time believing or accepting or experiencing pure non-duality.
Remember as the Course says, a universal theology is impossible but a universal is experience is possible and necessary. The truth is an experience. And whatever you believe the truth is, that will be your experience. So if you're quite convinced that the world you seem to be in is real, and that it objectively exists, and you live in it in a state of semi-consciousness believing it is your home and where you belong, having been created by it and destroyed by it, then regardless of your grasp of metaphysics you will not REALLY believe that there is only Oneness.
The result of that is, that no matter how someone explains it, you will never be able to accept that there is no world or that only Oneness is real. So then you're going to get into a state of mind where you are trying to be open to this extraordinary truth, which seems to defy and completely cancel this entire world, while at the same time holding onto and wanting this world to continue existing as reality.
So you will then be torn, and you will not be able to reconcile these two thought systems. The thought system of the ego - that the world is real, is completely 100% incompatible with, and opposite to, the thought system of the Holy Spirit, which recognizes that there is no real world here at all.
As you attempt to incorporate or learn some of what the pure-non-duality is teaching, or what God's truth is, yet while still quite strongly being convinced that the ego's truth (that the world is real) is still true, and not wanting to give up that truth in order to accept the pure-non-dual truth, you will just be in a tug of war with yourself. You will be in conflict.
You will not be able to reconcile and house the two thought systems in your mind at the same time. It will make you confused and disoriented and scared that you are losing touch with reality or sanity.
Your only possible conclusion, at that point, is that you cannot understand HOW it is possible for the pure-non-dualistic Course to be true, given that this other stuff you believe seems to also be true. You can't have them both be true, but your un-readiness to completely relinquish the ego beliefs makes you un-ready to accept the Holy Spirit's viewpoint. You cannot experience the truth of it, because it's too far outside of your envelope of what you will allow into your mind.
People who are quite far from the awareness of God will therefore have quite a skeptical, difficult time comprehending, accepting, or being open to, these very high metaphysical ideas and claims. They will see them as barely believable and quite false. By believing that the ego's world is the truth, i.e. real, you will automatically believe that God's world is false and unreal. You will not believe in it. So then you'll be just in this state of defending what you already think the truth is, confused about how it can be possible that God's truth is true (only the truth is true), at the same time as retaining what you already believe.
You have to therefore be willing to give up the ego belief in order to become more convinced that ACIM's claims are true. Few can truly, deeply believe that the entire world is not even real. That it is basically just a dream, a vast illusion, which seems very real but isn't at all. That takes a significant amount of purification and surrender and relinquishment of the entire ego though system, which is not something you can just do overnight typically.
Coming to an awareness of, and therefore experience of the truth, is going to take a long-term process, a lot of willingness, a lot of letting go, a lot of openness to questioning whether what you believe currently is really true, and gradually the truth will dawn on the mind and become acceptable. You cannot accept or believe what the Course is really saying if you believe, for example, that sin and guilt are real and irreversible, let alone your beliefs that your house and your car and your family and your job and your neighborhood are all allegedly "real" but are in fact not real.
It sounds as though your friend is afraid that they will lose something of value by believing the pure-non-duality of the Course. They see the ego world as valuable, meaningful, filled with truth and reality. They are attached to the world and to their body and to their ego identity. They fear that the truth has come to threaten them and topple their world.
So they likely have fallen in special-love with flowers and sunsets and rainbows and puppies and kittens and special foods and lovely places and certain special people, all of whom are ways that they believe this world is real and important and special. And that specialness is a substitute for the love of God, and a counter-attack on the truth. So, that person is going to have to find some willingness to look at EVERYTHING in their life and question its validity, reality, purpose, value and meaning.
Coming to the truth is not done by half. It really does entail the complete overhaul of your entire thought system, your whole way of thinking and perceiving, the questioning and undoing of every single form of specialness and ego, and the total healing of absolutely every hurt ever experienced.
What you will find as you proceed on this journey to accepting the truth, is that your relationship of specialness with the world will start to be replaced with a relationship of holiness. That means, you will start to see through and become disillusioned with and rejecting of the things that you thought were valuable, but which are not in truth.
What you used to experience as special and important will be let go, i.e. the egoic sense of specialness will be withdrawn. But in its place, since this is removing the blocks in the mind to the awareness of Love's presence, a light in you will begin to shine. And this light will be a light of joy and happiness. It will come from within and extend outwards, instead of your special belief that happiness begins outside of you and affects you positively.
Therefore you will find yourself freer, less encumbered, happier for no external reason, more at peace, less dependent on illusory forms of value, and more detached from your special relationships. Yet, this also will mean that whatever you are doing, you will be doing it with more joy and happiness and freedom. So you may actually be able to more genuinely and authentically enjoy whatever it is that you're doing.
This is of course a buildup to the "happy dream" where your interpretation of this illusory world as sinful is replaced with an interpretation that it is innocent. What's really taking place is that you are having a different relationship with yourself, based in love and forgiveness, and therefore your perception of the world reflects that.
This will lead you to to True Perception, i.e. the forgiven world. And then the world will disappear, because as Jesus describes, the purpose of True Perception is only to see the world as forgiven and unreal, and then it will disappear from sight, replaced with the Vision of God.
So your way of experiencing and enjoying the world will transform as you begin to take steps towards accepting that Oneness is real. You do not have to sacrifice. You do not have to try to change your behaviors in order to get rid of values that you are starting to see as false. Nobody is coming along to tell you to give up your egoic pleasures or your favorite foods or your best music. You will not be able to give these things up while your ego is falsely valuing them and is attached to them as a defense against the truth.
If you try to force yourself to get rid of such things, parts of the world, before you are genuinely accepting of their lack of value, you will perceive it as a sacrifice, and you will suffer and feel a sense of loss and grief. You do not need to do that, but most people do that because they do not as yet understand that the Course itself is not calling for sacrifice.
The ego that still persists in their mind believes strongly in sacrifice and as the "ego thinking" starts to mix with the "Course thinking", a tremendous number of misunderstandings and misapplications will arise, calling for you to get rid of stuff in your life that your ego deems "too ego" or "not spiritual". This will be a mistake, and it will hurt you and make you feel like you're ceasing to exist etc.
It's okay for example to still have money and property and object and toys and relationships and to go do those thoroughly egoic activities that your ego loves. But you need to learn that it does not mean you are guilty, and initially the ego's interpretation of the Course's truth will attempt to use the Course against you as an attack, calling for you to be guilty every time you have an ice-cream or want to watch your favorite tv show or have sex or whatever.
Gradually you will sort out what is true from what is false, what is ego from what is truth, and will become clearer about the fact happiness is shared with God, within your mind. And your willingness to accept this and to express it, allows you to seem to enjoy what the world has to offer, temporarily, while you're still progressing in your awakening.
At some point, you will learn to recognize what the world really IS offering, and will recognize its limitation, and the fact that it does not do anything to you, and the fact that it isn't really real, and that it does not hold any real value at all. These are just recognitions of the truth, replacing the illusions and lies you told yourself about how important this world seemed to be.
In the recognition of the truth, you will simply see the world for what it is - nothing real and nothing of value. This is why the Course says "This world holds nothing that I want". You will simultaneously, paradoxically, see with love and joy, but what you will see here is a world that is just an illusion, and is not the source of any of what you are experiencing. You are not happy because of objects and toys and people, you are happy because God is in your mind.
Eventually this will lead you to realize that the world is beautiful, as an illusion, as a forgiven innocent world, as a world which has never done anything to you, and as a world which does not really exist anyway because the separation never happened. And then you will let it go completely and it will disappear from sight. Your awareness will shift entirely to be fixated on God in pure perfect truth, and you will EXPERIENCE the truth and know it to be real.
In that light, you will never again be able to believe in an illusory world which you once thought had come to take the place of love. You will never again be able to value it in place of or as a substitute for God's love. You will never again believe that it offers you something better than the infinite abundance that God is sharing with you. And you will see no meaning in it that even begins to come close to the heartfelt meaningfulness of God's love for you, and yours for Him.
Only the truth is true. God is everything you really want. Enjoy the ride, while it lasts. Transform your perception. See the world for what it is, see it with love, and then disappear it. There is so much more to enjoy in God than this world could ever offer you.