tasmād yasya mahā-bāho
tasya prajñā pratiṣṭhitā
tasmāt—therefore; yasya—of one's; mahā-bāho—O mighty-armed one; nigṛhītāni—so curbed down; sarvaśaḥ—all around; indriyāṇi—the senses; indriya-arthebhyaḥ—for the sake of sense objects; tasya—his; prajñā—intelligence; pratiṣṭhitā—fixed.
Therefore, O mighty-armed, one whose senses are restrained from their objects is certainly of steady intelligence.
As enemies are curbed by superior force, similarly, the senses can be curbed not by any human endeavor, but only by keeping them engaged in the service of the Lord. One who has understood this—that only by Kṛṣṇa consciousness is one really established in intelligence and that one should practice this art under the guidance of a bona fide spiritual master—is called sādhaka, or a suitable candidate for liberation.
Link to this page: https://prabhupadabooks.com/bg/2/68