A man gives way to grief; he weeps. Or he is afraid. Or he is overcome by lust. What does all that mean? It means that he has not attained Chittasuddhi. It is only if one is free from sorrow, anger, Just, delusion etc. that one can come into direct communion with God. To get chittasuddhi each one must do his proper karma. 'You are a Kshatriyas', says the Lord, so, do your karma. Fight'.
‘Siddhim praapto yadaa brahma tadaapnoti nibodha me samaasenaiva kaunteya nishtaa jnaanasya yaa paraa.’
'I shall then tell you how the realization of the Supreme which is the' goal of jnaana ensues upon the attainment of chhtasuddhi. Chittasuddhi leads to Yogasiddhi, which in turn paves the way to jnaanasiddhi. Upon the attainment of the final stage of jnaanasiddhi, one realizes the Supreme; he is transformed into that Supreme. Speech itself is stilled there; for, there is no other to speak to in that stage. So, at the stage of Perfection there is no distinction of friend or foe.
There is no second there. Where there is no second, there can be no action. When one attains to that Universal, tasya kaaryam na vidyate, there is nothing for him to do. For, action requires a duality predicament.
But in the context of Arjuna's mental condition before the commencement of the war, his duty was to perform his karma and he could attain chittasuddhi only by doing his karma. He will then not grieve thinking he is injuring some one. He will stop weeping. He will be set on the road to Perfection. The first stage of that road is doing karma.