Verse 2.2.12

एको वशी सर्वभूतान्तरात्मा एकं रूपं बहुधा यः करोति ।
तमात्मस्थं ये'नुपश्यन्ति धीरास्तेषां सुखं शाश्वतं नेतरेषाम् ॥ १२ ॥

eko vaśī sarvabhūtāntarātmā ekaṃ rūpaṃ bahudhā yaḥ karoti |
tamātmasthaṃ ye'nupaśyanti dhīrāsteṣāṃ sukhaṃ śāśvataṃ netareṣām || 12 ||

12. Sole, controller, the internal atman of all living things who makes his own form diverse to the intelligent who realizes him as seated in the self, eternal bliss is theirs, not others.

Shankara’s Commentary:

Com.—Moreover, he, the lord of all, all-pervading, independent, is one (there is none other equal to him or greater than he); vasi ] under whose control all the universe is; because he is the internal atman of all; for, he makes himself though one, of the nature of unalloyed pure knowledge, diverse by the differences of impure conditions of name, form, etc., by his mere existence, having unthinkable powers. Âtmastham ] clearly perceived in the form of knowledge, in the conditioned intellect, in the akasa of the heart, within the body; for, the body is not the supporter of the atman, he being formless as the akasa. He is like the face reflected in the mirror. To those discerning persons who perceive this lord, this atman, all their external activities being checked in accordance with the teaching of the preceptor and the agamas and realise him directly, to those who have become lords of all, belongs the eternal bliss, i.e., delight in self and not to the undiscerning others, whose intelligence is engrossed by external objects, though the bliss is their own atman, which in the case of the latter is concealed by ignorance.