Krishna says that whose mind and intellect are established in 'that' (spirit) and whose sins have been dispelled by awareness reach a state of no return (5.17).
Unaware living is like living in darkness, where we keep falling and hurting ourselves. The next level is like experiencing some flashes of light where one attains awareness for a moment but falls back into ignorance. The final stage is like having permanent light like sunlight where the awareness attains a critical level and one never returns from there. This state of no return is also referred to as moksha, the ultimate freedom. It's not 'my' freedom but freedom from 'me' as all suffering is because of 'me'.
Samatva (equanimity) happens when one attains the state of no return and in this regard, Krishna says that the wise view a learned and cultured Brahamana, a cow, an elephant, and even a dog or dog eater as the same (5.18). Samatva is one of the foundational pillars of the Gita.
Realizing self as the self in all beings (5.7) is at the core of Samatva. It's recognizing that others too have good like us and we too have negatives like others. The next level is the ability to see the apparent contradictions or differences as equal, like seeing an animal and an animal eater as the same. It's dropping hatred (5.3) and dislikes which are products of ignorance. It's applying the same justifications for our gains as well as losses. Samatva is just a feeling which comes through awareness. The karma that flows out of an imbalanced mind is bound to bring misery.
Krishna assures that even here (in this world and at this moment), the dualities of manifested existence (birth/death) have been overcome by those of equal/impartial mindedness and will be established in Brahman (Absolute) who is faultless and impartial (5.19).
Source - Daily World