अनादित्वान्निर्गुणत्वात्परमात्मायमव्ययः ।
शरीरस्थोऽपि कौन्तेय न करोति न लिप्यते ।। १३.३१ ।।

anāditvān-nirguṇatvāt-paramātmāyam-avyaya: |
śarīrastho’pi kaunteya na karoti na lipyate || 13.31 ||

This is so far as the inner expansion of the Knower is concerned. The quality or excellence called unaffectedness is something distinct:

The inmost Soul, being beginningless and free of any attribute, is Imperishable. Though dwelling in the body, it neither does anything nor gets tainted the least.

Transcending all materiality and its laws and processes, this inner Soul, the paramātmā, is truly without any kind of involvement or affectation. Being so, it remains imperishable, untouched by anything whatsoever, be it activity or otherwise. Though it is found to be associated with the body, unlike the body it acts not, and hence is not tainted at any time. Complete blemishlessness is its nature.

What does this mean? The description of the inmost Soul becomes characteristic of the Knower. Knowing his own core to be like this, the Knower thus is able to disengage himself from identification with his body, and view it as any other object. Thereby he becomes free of all kinds of bondage and involvement.

Birth is what the body undergoes. The Knower knows that he is devoid of birth. Consequently he is equally devoid of growth, actions and their consequences. Where is then any question of bondage or stain? Let the body be. But all it does has hardly anything to do with the supra-material core within.

Earlier also Krishna had referred to the same unaffectedness (5.8,9): Whether seeing, hearing, touching, smelling, eating, walking, sleeping, speaking, leaving, holding, winking or opening – it is all an interplay of the senses and the sense-objects. The Soul, as different from the body, remains different all the time and hence is not touched or tainted at all!