When anyone becomes established in Yoga, then the self becomes uplifted from the multitude of mundane evils by that very self. Therefore,
उद्धरेदात्मनात्मानं नात्मानमवसादयेत् ।
आत्मैव ह्यात्मनो बन्धुरात्मैव रिपुरात्मनः ॥ ५ ॥ (6.5)
One should uplift one’s self with the mind; one should not lower the self. For, one’s mind is verily the friend of one’s own self as also the enemy of his own self.
आत्मना, with the self, with the mind imbued with discrimination; उत्-हरेत्, one should lift (हरेत्) up (उत्); आत्मानम्, one’s self, from that sea of the world in which it is drowned; i.e. one should bring about its establishment in yoga by totally giving up attachment to objects.
But न अवसादयेत्, one should not lower, drown in the sea of the world; आत्मानम्, the self, through attachment to objects.
हि, For; आत्मा एव, one’s mind, verily; is the बन्धु:, a friend, benefactor, cause of Liberation from the bondage of the world; आत्मन:, of one’s self; not so anyone else whosoever, because even a friend in the world becomes a source of bondage on account of love.
आत्मा एव, one’s mind, verily; not anyone else; is the रिपु:, enemy, the perpetrator of evil, because like a silkworm it enters into the cell of bondage of the sense-objects; आत्मन:, of one’s self.
Since mind is one’s own maker of even an external enemy, therefore the emphatic statement, ‘one’ mind is verily the enemy of one’s self, is reasonable.
Now Sri Krishna states what kind of ‘self’ becomes the friendly self and what kind of it becomes the enemy of the ‘self’.
बन्धुरात्मात्मनस्तस्य येनात्मैवात्मना जितः ।
अनात्मनस्तु शत्रुत्वे वर्तेतात्मैव शत्रुवत् ॥ ६ ॥ (6.6)
Of him by whom the aggregate of his body and organs has been conquered by the mind itself, his self becomes the friend of himself. But for one who has not conquered the aggregate of his body and organs, his self itself would act inimically like an enemy.
तस्य, of his; येन, by whom; आत्मा, the self, the aggregate of his body and organs; जित:, has been conquered, brought under his own control;
आत्मना एव, by the self itself, by the mind itself that is endowed with discrimination, but not brought under control with weapons etc; आत्मा, his self, by himself; becomes बन्धु:, the friend; आत्मन:, of himself; because on account of its absence of the aggregate’s unrestrained behavior, the aggregate becomes his benefactor.
तु, But; अनात्मन:, for one who has not conquered the aggregate of his body and organs; आत्मा एव, his self itself, he himself indeed; वर्तेत, would act; शत्रुत्वे, inimically; शत्रुवत्, like an enemy; because like an external enemy one would be doing harm to oneself on account of one’s unrestrained behavior.
Sri Krishna explains how one who has conquered the aggregate of one’s body and organs is one’s own friend as follows:
जितात्मनः प्रशान्तस्य परमात्मा समाहितः ।
शीतोष्णसुखदुःखेषु तथा मानापमानयोः ॥ ७ ॥ (6.7)
To one who has control over the aggregates of one’s body and organs and who is serene even in the presence of cold and heat, happiness and sorrow, as also honour and dishonour, the supreme Self becomes the content of Samaadhi.
To the aforesaid जितामन:, one who has control over his body and his organs;
प्रशान्तस्य, who is serene, who with the sameness of outlook everywhere is devoid of attachment and aversion; even in the presence of, or, as a result of equanimity with regard to सीत-उष्ण-सुख-दुक्खेषु, cold and heat, happiness and sorrow which are causes of mental disturbances; तथा, so also; even in the presence of or as a result of equanimity with regard to, मान-अपमानयोः, honour and dishonour, which are causes of mental disturbance; परमात्मा, the supreme Self, the Self which is by nature self-effulgent Consciousness; समाहितः, becomes the content of समाधि. He becomes established in Yoga.
Or the conjunction in परमात्मा is to be split up, परम्, alone and आत्मा, Self; Only जितात्मनः प्रशान्तस्य, of the self-controlled and serene person; परम्, alone; does आत्मा, the Self; become समाहितः, absorbed in समाधि; not of anyone else.
So one should have control over the body and its organs and become tranquil. This is the meaning.