A philosophical premise rooted in the mystic arts of Alchemy and Yogic Meditation.
"NonDual" is a self-realization in the early stages of Enlightenment where the illusion is broken and the individual begins to recognize his existence is NOT solely as an "individual". Metaphysically AND physically; he is a slice of a larger whole.
This "Spiritual Awakening" is profound and humbling, as it forces one to reconcile the state of ignorance they have lived up to that point.
This newfound "reality" causes a psychological paradigm shift which involves many internal reviews and reorganization of values and beliefs. It takes constant Awareness to integrate these realizations about the Self, to work towards becoming better internally.
You can't lie to yourself in this work, that's literally what you are trying to overcome. Disillusioning.
This process is also extremely disorienting. Deep feelings of depression, disillusionment (from the illusion you were suffering), and depersonalization. The Dark Night of The Soul. It's difficult to feel profoundly removed from society, and still put the effort into rejoining the world from this new cosmic perspective.
I should mention, it's also the most empowering thing you can experience in this Life.
There is no other human experience that compares with overcoming the true depths of that existential dread we all hide our faces from. It's like standing outside of the universe, looking in.
The wisdom of reality is a monster in your closet... that just wants to hug you and help you. Showing you where you're going wrong, and pointing out the path to becoming better. Better for the benefit of yourself, and in-turn a beacon to the unconscious world still wandering blindly in the dark.
So this one goes out to all Dark Nighters who have pressed on with their Self-Mastery and are Becoming. Many may not understand what this tee means, but you should be used to that by now.
"There are within man faculties of the soul which, if developed, will enable him to perceive this inner world, so that it will become possible for him to explore and to study it precisely as man has explored and studied that part of the world which is within the reach of all.
These faculties are the heritage of the whole human race; they will unfold within every one of us as our evolution progresses; but men who are willing to devote themselves to the effort may gain them in advance of the rest, just as a blacksmith’s apprentice, specializing in the use of certain muscles, may attain (so far as they are concerned) a development much greater than that of other youths of his age.
There are men who have these powers in working order, and are able by their use to obtain a vast amount of most interesting information about the world which most of us as yet cannot see.
Let it be clearly understood that there is nothing fanciful or unnatural about such sight. It is simply an extension of faculties with which we are all familiar, and to develop it is to make oneself sensitive to vibrations more rapid than those to which our physical senses are normally trained to respond."
~ C. W. Leadbeater ~
(Author: The Astral Plane / 1898)