The constancy by which one sustains the activities of the mind, the prāṇa and the senses, through unwavering yoga — that constancy is sāttvic, oh Pārtha.

Sāttvic constancy (dhṛti): sustains (dhārayate) the activities (kriyāḥ) of mind, prāṇa and senses.

Yogena avyabhicāriṇyā — through unwavering, non-deviating yoga. It is firmness in practice, stable discipline, determination toward the spiritual goal.