Sanskrit
बुद्ध्या विशुद्धया युक्तो धृत्याऽऽत्मानं नियम्य च । शब्दादीन्विषयांस्त्यक्त्वा रागद्वेषौ व्युदस्य च ॥ ५१ ॥
buddhyā viśuddhayā yukto dhṛtyātmānaṃ niyamya ca śabdādīn viṣayāṃs tyaktvā rāga-dveṣau vyudasya ca
Translation
United to this Reason, purified, controlling the self by firmness, having abandoned sound and the other objects of the senses, having laid aside passion and malice,
Annie Besant · The Bhagavad-Gita, translated by Annie Besant (4th ed., 1922) — Wikisource · Public Domain
Explanation
The description of the Brahman-bound life begins with intellectual and volitional groundwork — purified reason (buddhi), firmness in self-governance, and the deliberate abandonment of sense-objects along with passion and malice. This is the same buddhi chapters 2 and 3 already identified as the seat of discrimination and steadiness, sthitaprajna territory; what’s added here is that this discriminating faculty must first be purified before it can carry the weight of the sequence that follows across verses 52-53.