Arjuna wishes to know the true nature of what the word 'renunciation' (sannyasa) means, and likewise the true nature of what the word 'relinquishment' (tyaga) means, and to know them separately, each marked off from the other. He addresses the Lord as Hrishikesha and as the slayer of Keshin, for a certain demon named Keshin had taken the disguise of a horse and was destroyed by the Lord Vasudeva. The words 'renunciation' and 'relinquishment' had been used here and there in the earlier chapters without their sense being precisely settled. So, when Arjuna asked for that to be settled, the Blessed Lord spoke.
Contemporary English rendering of the Sanskrit bhāṣya, pending scholar review.