Bg 2.48

yoga-sthah kuru karmani
sangam tyaktva dhanañ-jaya
siddhy-asiddhyoh samo bhutva
samatvam yoga ucyate

Word for word: 
yoga-sthah — equipoised; kuru — perform; karmani — your duties; sangam — attachment; tyaktva — giving up; dhanam-jaya — O Arjuna; siddhi-asiddhyoh — in success and failure; samah — equipoised; bhutva — becoming; samatvam — equanimity; yogah — yoga; ucyate — is called.

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Perform your duty equipoised, O Arjuna, abandoning all attachment to success or failure. Such equanimity is called yoga.

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Krishna tells Arjuna that he should act in yoga. And what is that yoga? Yoga means to concentrate the mind upon the Supreme by controlling the ever-disturbing senses. And who is the Supreme? The Supreme is the Lord. And because He Himself is telling Arjuna to fight, Arjuna has nothing to do with the results of the fight. Gain or victory are Krishna’s concern; Arjuna is simply advised to act according to the dictation of Krishna. The following of Krishna’s dictation is real yoga, and this is practiced in the process called Krishna consciousness. By Krishna consciousness only can one give up the sense of proprietorship. One has to become the servant of Krishna, or the servant of the servant of Krishna. That is the right way to discharge duty in Krishna consciousness, which alone can help one to act in yoga.

Arjuna is a ksatriya, and as such he is participating in the varnasrama-dharma institution. It is said in the Visnu Purana that in the varnasrama-dharma, the whole aim is to satisfy Visnu. No one should satisfy himself, as is the rule in the material world, but one should satisfy Krishna. So unless one satisfies Krishna, one cannot correctly observe the principles of varnasrama-dharma. Indirectly, Arjuna was advised to act as Krishna told him.