mahatmanas tu mam partha
daivim prakrtim asritah
jnatva bhutadim avyayam
O son of Prtha, those who are not deluded, the great souls, are under the protection of the divine nature. They are fully engaged in devotional service because they know Me as the Supreme Personality of Godhead, original and inexhaustible.
In this verse the description of mahatma is clearly given. The first sign of the mahatma is that he is already situated in the divine nature. He is not under the control of material nature. And how is this effected? That is explained in the Seventh Chapter: one who surrenders unto the Supreme Personality of Godhead, Sri Krishna, at once becomes freed from the control of material nature. That is the qualification. One can become free from the control of material nature as soon as he surrenders his soul to the Supreme Personality of Godhead. That is the preliminary formula. Being marginal potency, as soon as the living entity is freed from the control of material nature, he is put under the guidance of the spiritual nature. The guidance of the spiritual nature is called daivi prakrti, divine nature. So, when one is promoted in that way--by surrendering to the Supreme Personality of Godhead -- one attains to the stage of great soul, mahatma.
The mahatma does not divert his attention to anything outside Krishna because he knows perfectly well that Krishna is the original Supreme Person, the cause of all causes. There is no doubt about it. Such a mahatma, or great soul, develops through association with other mahatmas, pure devotees. Pure devotees are not even attracted by Krishna's other features, such as the four-armed Maha-Visnu. They are simply attracted by the two-armed form of Krishna. Since they are not attracted to other features of Krishna (what to speak of the demigods), they are not concerned with any form of a demigod or of a human being. They only meditate upon Krishna in Krishna consciousness. They are always engaging in the unswerving service of the Lord in Krishna consciousness.
(Bhagavad-gita As It Is 9.13, Purport)