The famous phrase by Patanjali from where Patanjali Yoga Sutras begins.
I have read a few books about yoga, yoga sutras, Raja Yoga, Karma yoga, books on yoga by Baba Ramdev, and a few others, which served as good appetizers for a further inquisitive thinking on the subject.
Yoga means union of every opposite poles into oneness, and conciliation of everything to merge into an infinite, eternal, and blissful universal soul. The aim of yoga is conciliation and oneness, but its path crosses from the ocean of retribution, where the subject passes through the awards and deterrence inflicted by opposite forces depending on his level of evolution, where the subject is consumed and destructed, and rebuilt again, an ongoing cycle which culminates in ultimate dissolution of the subject.
Each element of the nature has its opposite counterpart, like fire and water, anger and calmness, poison and nectar, and so on. When the practices in the books mentioned above, like meditation, and twisting of bodies is initiated, all these opposite forces initiates a war against the other opposites, and a process of destruction initiates as our human form is direct replica of the world outside. There may be instances when the subject does not have direct experience of this destruction because of lack of command over the subconscious or unconscious parts of the mind, but these wars takes place and destructs the finite form, and an infinite and eternal entity is born, free from the circus of life and death.
There is no distinction between body, mind and soul, and everything is destructed to merge into what can be called god consciousness. Imagine a bubble, each one of us are living inside one such bubble, with our personal identities and inhibitions, we need water to quench our thirst, we need food to overcome hunger, in short, we have a finite existence which is dependent on the external influences to incite the emotions of pleasure, pain, and happiness among us. The aim of yoga is to shatter these limited personal identities and inhibitions, and dissolve into a state where there is no thirst or hunger for anything, no aspirations, and no aim, we have everything that we want.
The intent of performing actions is material here, every action must be performed without any aspiration for gain of any type, and doing them with utmost involvement, without being perturbed by any outcome.