Know that to be yoga, inner spiritual communion, which is free from the touch of grief. With unswerving resolve, with a mind unsmitten by dejection, such yoga has to be pursued.
Krishna, in a way, gives a new description of yoga. He had indicated that when the intelligence, tossed by the numerous statements of Vedas, is able to remain still and poised, not ruffled by secular or spiritual distinctions, then it will attain yoga (2.53). It was on hearing this that Arjuna enquired about Sthita-prajµa and Sthita-dhee.
Here he defines yoga as a state, which grief touches not. Just as one swimming in water is not affected by its drowning power, so too the yogi will interact with the world, assimilating all interactional impacts, getting enriched and empowered every time. He will have no dejection or other adverse notes.
His mind will reach a brilliant state of purity and stability. Instead of worldly impacts overpowering him, his mind will overwhelm them all. The seeker should strive for this kind of inner yoga pursuit.