In plain words
is concentrated, one can do that work exceedingly well. Whether in worldly affairs or on the spiritual path, in any matter or any task whatsoever, the more one's concentration grows, the greater the result one can obtain in that task, and the better the task itself is carried out. This, indeed, is the very key that unlocks the treasury of knowledge. One must say that this power of concentration alone is, in raja yoga, the one essential thing. Countless unwanted thoughts force their way into the intellect and throw it into confusion. To resist them and hold such a mind firmly under one's own control, raja yoga alone is the refuge.
Now, the last of the four is jñāna-yoga. Here, what predominates is a complete inquiry into truth itself. The jñāna-yogi holds to convictions that transcend this world, which he sees as a mere fabrication of appearances; no object, no task, and no person in the world can ever satisfy him. Indeed, he means to rise even above life's ordinary daily routines. Afloat, as it were, on the great ocean of his faith in God, every worldly object appears to him like a relative. He yearns, above all, to reach the goal, the centre, the very crux that is the root of everything — he strives to become Satya itself, unwilling to remain separate from it, refusing ever to think of it as something apart. To him, God alone is his every kinsman, and he holds no other worry, no other attachment, no other desire: all, to him, is God. Whether it brings difficulty or comfort, gain or loss, he longs to experience, without distinction, the state of non-dual vision — and that alone is true Jñāna. To one who holds such a conviction, the thought arises that the whole universe is an insubstantial, illusory show. And yet the senses, now and again, drag that very conviction back down, striving to plunge him into worldly delusion. But, keeping his senses under the most careful control, pushing that pull aside however he must, he seeks, step by step, to draw nearer and nearer to God.