It's the complete and permanent dissolvement/cessation of all concepts, thoughts, and thinking of the ego/mind.
It's the letting go of the very energy behind thoughts and thinking.
It's the actual death of the thinking process of the mind. The individual's self/ego/I literally dies. What you currently consider to be "me", dies, and is no more.
The ego/mind fears that life/existence will end when IT comes to an end, but this isn't true.
It's the realization of what one already is, always was, and always will be, which is changeless and unlimited.
It's the realization of Self as All of Existence, which is Pure Awareness, which is beyond all form, shape, dimension, time, concepts, and the physicality of this world.
It's simply the letting go of the emotions, thoughts, and thinking that mask and stand in the way of the Infinite Intuitive Knowingness and Awareness of Absolute Truth.
It's for those who seek absolute and permanent completion, wholeness, perfection, freedom, peace, happiness, joy, bliss, etc.
It's a profound ineffable love, peace, stillness, and silence beyond bliss and ecstasy, which is well beyond words and description.
It's an innate knowingness of the truths of the universe, because if "one" is Everything, then naturally, "one" knows everything.
It precludes individual will, intentions, desires, wants, "needs", emotions, personality, thoughts, ideas, concepts, and thinking.
It's not the denial of will. It's for those who wish to serve the world/universe in the highest possible way, whatever that may happen to be, in this very moment, right now.
It's for those who want to let go of the little self; the me, myself & I, which is the source of all problems and suffering.
Purposefully creating worldly "success" with thought (the law of attraction) is one goal, while moving beyond thought totally is a different goal altogether. One helps us cope with this physical world, while the other takes us beyond it forever (no more reincarnation). One perpetuates individual karma (positive & negative), while the other frees us of it permanently. "The truth shall set you free."
Some people believe various psychic abilities, siddhis, and occult powers are "spiritual", but the truly Enlightened, such as Ramana Maharshi, warn otherwise and say "Forget about siddhis. They are all manifestations of the duality, therefore illusory. Do not seek them. It's immaterial to spiritual realization. Find out who you are."