And the same theme Krishna will repeat elaborately in last verse of this section.

BG 2.53

sruti–vipratipanna te

yada sthasyati niscala

samadhav acala buddhis

tada yogam avapsyasi

SYNONYMS

sruti — of Vedic revelation; vipratipanna — without being influenced by the fruitive results; te — your; yada — when; sthasyati — remains; niscala — unmoved; samadhau — in transcendental consciousness, or Krishna consciousness; acala — unflinching; buddhih — intelligence; tada — at that time; yogam — self-realization; avapsyasi — you will achieve.

TRANSLATION

When your mind is no longer disturbed by the flowery language of the Vedas, and when it remains fixed in the trance of self-realization, then you will have attained the divine consciousness.

When one hears about the eternal spiritual truth, and after hearing about the eternal spiritual truth, if the śruti is saying about the fruitive activities, yadā sthāsyati niścalā, one stays niścala, fixed and unshaken. Then, samadhau acala-buddhiḥ, one is not disturbed by fruitive activities and stays fixed in samadhi acala buddhiḥ.

So, it is interesting that Krishna is not saying Acāla-mana: Instead he is saying, samadhau acala-buddhiḥ, indicating that our mind becomes deluded because our intelligence is deluded. Once our intelligence is completely fixed, then the mind is also unable to shake us. Just as waves shake a boat, but if the boat is strongly anchored, it will not shake as much. Similarly, in samadhau acala-buddhiḥ, once we are convinced that Krishna is the ultimate goal, our intelligence will never be shaken. tadā yogaṁ avāpsyasi, at that time, we can realize that we have attained self-realization. Further, Krishna is outlining the characteristics of yoga that includes remaining undisturbed from everything material. Thus, we can stay fixed in the spiritual. When we are unaffected by the material world, we can understand that we are firmly established in the spiritual realm. Krishna’s teachings highlight how to practice Karma Yoga by maintaining equanimity amidst the fluctuations of material existence and remaining steadfast in the spiritual reality.