In the Gita, emphasis is again and again laid on developing that mental equipoise which is not disturbed either by adversity or by prosperity. This state can be achieved only by completely surrendering ourselves to God. Bhagavan makes this clear by directions like Yuktha Aaseeta Mat Para, Maamekam Saranam Vraja, and Vasudevassarvamiti. An Ayuktha, i.e., one who cannot view everything with equal unconcern and consequently whose mind is easily assailed by desires and passions and who is unable to do his duty in the spirit of dedication, neither profits from knowledge nor acquires a spirit of devoted surrender (Bhaavana). Without Bhaavana he cannot find peace (Saanti) and without Peace, he does not attain absolute happiness (Sukam). It is this teaching of the Gita that inspired Saint Thyagaraja to sing Saanthamu lekha Saukhyamu ledhu. If the mind runs after worldly pleasures, all efforts to find real happiness will go in vain like ghee poured in a leaky vessel. It follows that Yoga in the Gita sense is necessary both for acquiring Paroksha Jnana, knowledge of the Ultimate Reality, and Aparoksha Jnana, Realisation of that Reality.
It is to be noted that the Samatva or equal feeling in the context of Yoga does not denote universal equality, but only the capacity to treat good and bad results with the same feeling. The stress is on the performance of one's allotted duty. That duty should be performed well, without thought of reward and with devotion in the heart. While performing it, the act should be dedicated to God. This is not possible without the control of sense-organs. The Indriyas should be withdrawn from the objects which attract them. If they run away unbridle, the mind will also run away along with them. Such a wavering mind cannot contemplate the Atman within, by which process alone the ultimate Truth can be realised. When the mind is tossed by Indriyas, Prajna will go out of proper cores like a ship tossed by high winds in the ocean. The distinction made in the Gita between mind and Prajna is to be noted. In Sanskrit, the mind is known by different terms according to its functions, like thinking, deciding, contemplating, etc. The mind with the experience of inward contemplation is Prajna. In the above simile, the mind takes the place of the ocean, the ship is Prajna and the wind is the play of the senses.
Complete mastery of the senses is the foundation on which one has to raise the edifice of Stitha Prajnatva. When the functioning of the Indriyas is turned inwards, they get merged with the Atman within. The Atman is not affected thereby even as the ocean remains unaffected by the waters of the numerous rivers flowing into it. A person whose mind is so evolved is a Jnani. He is able to distinguish the real from the unreal and achieve the bliss that flows from the realisation of the all-pervasiveness of the Paramatma and the identification of the Atma with the Paramatma. What the worldly minded person imagines as real will be unreal for such a Jnani. So, Bhagavan wants Arjuna to do his duty, not with the object of gaining a Kingdom, but the object of acquiring the mental discipline which will enable him to attain the state of inaction, namely, Brahmanirvaana or the merger of the Atma with Paramatma.