"What is yoga?" is very often being expounded as, "Yoga is the union of the soul, the body, and the mind," for the minds that believe in the existence of an individual soul/spirit, or "Yoga is the union of the body and the mind," for the minds that don't believe in the existence of an individual soul/spirit, as well as, "Yoga is the union of the individual consciousness and the universal consciousness", or "Yoga is the union of 'this' and 'that'."
Due to these words, many minds interpret and understand as "The mind attains union with the body where the passionate egoistic wishful mind can have complete control or influence over the body to be the way that it desires, defying selfless impermanent changes of decay, aging, illness, injury, pain, weakness, and death/disintegration/mortality," or "The individual consciousness attains union with the universal consciousness where the passionate egoistic wishful mind thinks that it will attain immortality and can have the superpower to control or desire everything to be the way that it desires, untouched by the nature's law of cause and effect, being the master of the selfless elements and energy, to be existing infinitely and unconditionally in a limitless 'pleasant desirable space', or 'perfect world', or 'infinite absolute existence', that is all desirable, pleasant, and enjoyable, where there is still the existence of an idea of 'I' in the form of thinking or a continuous stream of countless thoughts in the modification of the mind, that has such wishful desire waiting to be gratified, that doesn't desire to be here that is being perceived as imperfect and undesirable, while desire to be somewhere else that is perfect and desirable, by trying to be reuniting and be identifying with a higher and purer super powerful absolute entity or infinite existence for achieving all that."
The selfless thinking mind is merely part of the selfless function of the selfless body. There is no 'union', as the body and mind were never two separated 'thing', and it's merely a selfless and impermanent limited adjunct supported and powered by selfless elements and energy. Without the existence and function of the body, there's no existence and function of the mind. And, if without the selfless support of the supportive elements and energy for being what they are, the body and mind cannot and doesn't exist, not to say, to be functioning.
The presence of ignorance and the idea of 'I' in the modification of the thinking mind generates the sense of separateness or distinction between 'I' and what is not 'I'. While in many different kinds of belief, the minds believe that there's an immortal infinite individual 'soul/spirit' that is pure and perfect, of who all and everyone really are, residing in the mortal physical body that is impure and imperfect, and via the function of the perceptive cognitive intellectual emotional thinking and acting mind to be experiencing a worldly life existence perceiving names and forms of sights, sounds, smells, tastes, and sensations through the organs of the senses, and performing actions through the organs of actions, where the 'soul/spirit' (pure and immortal, and that is who I really am), body and mind (impure and mortal, and that is not who I am), are distinctive from one another. Under this belief, yoga is being interpreted as "The union of the 'soul/spirit', the body, and the mind," so that I am the one in control of the body and mind to be the way that I desire it to be, and not under the influence of the elements and energy, defying selfless impermanent changes and the nature's law of cause and effect.
Instead of expounding yoga as "Yoga is the union of this and that," but expounding yoga as it is, "Yoga Citta Vriti Nirodhah."
It is about the annihilation of the restless modification (thought activities) of the selfless mind, or Silence, devoid of thought activities/names and forms/desires/actions, or devoid of the idea of 'I', or devoid of the ignorant non-existing individual identification of a permanent independent individual identity/being/existence, where the selfless thinking mind attains self-realization towards non-separateness or oneness (which is nothing to do with "the union of this and that") upon the realization of selflessness and impermanence, where there is no 'I' existing, or there is not an infinite existence of a permanent independent unchanging immortal individual identity of anything, where all and everyone and everything are the same selfless and impermanent.
The only momentary existence, is in NOW, and it's constantly changing, where there is a beginning and an end of this selfless impermanent momentary limited conditional existence, where there's no infinite immortal 'I' existing to be under going selfless impermanent changes in any particular selfless impermanent names and forms, under the influence of the many different selfless elements and energy that are supporting and influencing all kinds of names and forms arising, changing, and passing away (forming, decaying, and disintegration), selflessly.
There is no 'I'. Who, or what is there to be attaining union with this or that? Who, or what is there to be desiring or not desiring this or that? All and everything are merely selfless and impermanent names and forms that exist momentarily in this space that doesn't belong to anyone or anything under the selfless and intentionless support and influence of the selfless elements and selfless energy.
Even though the thinking and acting mind is only existing and functioning momentarily in this world through the selfless body of the selfless senses, the selfless organs of the senses, and the selfless organs of functions and actions, but it can create so much actions and consequences of actions out of ignorance, egoism, impurities, and restlessness, either intentionally or unintentionally, during its momentary existence, that give rise to so much unnecessary impactful damages and suffering unto oneself and others and the surrounding environment, that would be affecting all and everything in certain way.
That's why it is upmost important to free the mind from ignorance, the idea of 'I', egoism, impurities, and restlessness, even if the mind won't be able to create any ignorant actions and consequences of actions upon ceased existing, but the pleasant or unpleasant impact that it had been creating while momentarily existing and functioning will still be impacting the world that doesn't belong to anyone, in certain way, for certain extended period, after the selfless body and mind ceased existing.
"Mind conquest/Self-realization is the greatest duty of mankind." - Saints and Sages, Gurus and Buddhas, all the practitioners and teachers of Dhamma.Inquire the truth of everything.