Do we need the Mahabharata?
Actually, the Bhagavad Gita is part of the larger historical narrative of the Mahabharata. The Mahabharata provides the important contextual history of the battle at Kuruksetra and of the Pandavas and Kauravas. One can appreciate the Bhagavad Gita, the great conversation between Arjuna and Krishna, even more upon understanding their familial connection as cousins and upon learning about Arjuna’s glorious birth and activities, many of which intersect with Krishna and Balarama’s.
While it is true that we can perfect our bhakti practice through studying the Gita and through chanting alone, all of these other texts, including the Mahabharata, inform and inspire our practice. If the Mahabharata succeeds in attracting our minds to Krishna—and it has for many—than it is preeminently useful for us.