Gita 02.53 explained
And the same theme Krishna will repeat elaborately in last verse of this section.
samadhav acala buddhis
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.
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.
sruti-vipratipanna te, Even if one hears from scriptures and what one hears something which is different from what has been thought till now, vipratipanna te, till now one has heard about fruitive activities in result and now one hears about the eternal spiritual truth and after hearing about the eternal spiritual truth then if the Sruti is saying about something else about the fruitive activities, yada sthasyati niscala, one stays niscala, fixed unshaken then samadhav acala buddhis, one is not shaken by this and one stays fixed in Samadhi Acala buddhis.
So it is interesting Krishna is not saying Achala Mana; samadhav acala buddhis, so actually our mind become deluded because our intelligence is deluded, once our intelligence is completely fixed then the mind is also not able to shake us, when the waves will come the waves will shake the boat but if the boat is strongly anchored then the boat will not shake so much so samadhav acala buddhis, so once we are convinced that Krishna is the ultimate goal then the intelligence is never be shaken tada yogam avapsyasi, at that time you can know that you attain yoga, so here Krishna is giving characteristics of Yoga be undisturbed by everything material then you can stay fixed in spiritual, when you are undisturbed from material then you can also know that you are fixed in spiritual so in this way Krishna has talked about how to practice Karma Yoga by staying equipoised among material ups and down and stay fixed in spiritual reality.