The unwavering steadfastness by which one holds the activities of the mind, the vital breath and the senses in check through yoga — that steadfastness, O son of Pritha, is sattvic.
Explanation
Krishna is continuing his threefold classification of mental faculties, here turning to steadfastness or resolve (dhṛti), the inner power that keeps one's efforts from collapsing. The sattvic kind, belonging to the guṇa of clarity (sattva), is an unwavering resolve that keeps mind, breath (prāṇa) and senses steadily under control through yoga, meaning disciplined practice. Commentators differ on whether this yoga means meditation specifically or steady self-discipline more broadly, and the verse supports either reading.