Yoga is the most direct and also the most ample manifestation possible of a spiritual principle which, as such, must be able to reveal itself whenever the nature of things permits or demands it: this principle is essentially that of a technique – or an “alchemy  ” – designed to open the human microcosm to the divine influx. Yoga itself is defined as a “cessation of the activities of the mental substance,” and strictly speaking there is only one Yoga – the art of perfect concentration, of which Hatha-Yoga and Raja-Yoga are the two essential forms, and of which the other Yogas (Laya and Mantra) are special modalities or developments. It is true that the word Yoga also designates – in virtue of its literal sense of “Union” – the three great paths of gnosis (jnana), love (bhakti) and action (karma); but the connection with the principle that characterizes the yogic art is then much less direct. Yoga, as defined in the Sutras of Patanjali and related works, is always the interior alchemy, or the ensemble of technical means for realizing – with the aid of intellectual, corporal, moral and sometimes emotional elements – union through ecstasy or samadhi. [GTUFS: LSelf, A View of Yoga]

Yogic Principle: In reality, the yogic principle has its foundation in the cosmological aspect of man, an aspect that implies the possibility of applying to the microcosm disciplines which are “quasi-geometrical” and consequently as foreign to the circuitous ways of reasoning as to the impulses of sentiment; that is to say, these disciplines have a character that is purely “physical,” using this term according to its primitive sense as applying to the whole realm of “concordant actions and reactions,” hence to all that is subject to the impersonal laws and forces of the cosmos. On the other hand, when viewed according to a more profound perspective, the yogic principle is based on the idea that man is as though steeped in the Infinite: his essence – that by which he exists and knows – is “not other than” infinite just as a piece of ice is not other than the water in which it floats; man is “Infinity congealed” – if one can express oneself thus. It is our hardness alone, the opacity of our fallen condition, that renders us impermeable to the pre-existing Grace; the practice of Yoga is the art of opening – on the basis of our cosmic structure – our carapace to the Light which infinitely surrounds us.* (*But which is, practically speaking and doubtless, “within us.” “The Kingdom of God is within you,” said Christ. And if he enjoins praying that “Thy Kingdom come,” what is meant is not only universal regeneration, but also – and for all the more reason – the coming of the “Kingdom of Heaven” in our heart, which is like the point of intersection – or “strait gate” – towards the Infinite.) [GTUFS: LSelf, A View of Yoga]