anaaditvaannirgunatvaatparamaatmaayamavyayaha |
shareerasthopi kaunteya na karoti na lipyate || 31 ||

Without beginning, without qualities, this supreme self is indestructible. Though residing in the body, O Kaunteya, it neither acts nor is tainted.
anaaditvaat : without beginning
nirgunatvaat : without qualities
paramaatmaa : supreme self
ayam : this
avyayaha : indestructible
shareerasthaha : residing in the body
api : even though
kaunteya : O Kaunteya
na : not
karoti: act
na : not
lipyate : tainted
As this chapter slowly comes to a close, Shri Krishna begins to describe the nature of the supreme self. Since this chapter gives prominence to logic, more so than any other chapter in the Gita, he wants to clear any doubts or misconceptions that we may harbour about the supreme self. The first doubt we may have is as follows. If Prakriti is without beginning, and the supreme self is also without beginning, what makes them different?
Shri Krishna says that the difference is cause by whether or not they have gunaas or qualities. So far, we have seen that Prakriti is nothing but the three gunaas of sattva, rajas and tamas. But the supreme self is “nirguna”, it has no association or association with any quality whatsoever. This is what makes it different than Prakriti. Also, Prakriti is constantly changing and perishing whereas the supreme self is imperishable. When something has association with qualities, like the human body has strength, it is bound to perish or decay. Since the supreme self has no qualities at all, it is imperishable. Prakriti, on the other hand, is every changing and perishable.
Another doubt is as follows. Does the supreme self get affected by the actions and reactions of Prakriti? Shri Krishna asserts that it does not. We have seen that the supreme self, due to ignorance, identifies itself with a body, a product of Prakriti. This is what is referred to in this shloka – it “resides” in the body. We have also repeatedly heard that the supreme self has nothing to do with Prakriti. It can never become the doer or the enjoyer of any actions. But due to the apparent identification with the body, the supreme self assumes that it is a doer and enjoyer. Since the identification is fake, not real, the supreme self can never get affected by the actions and reactions by Prakriti.
We may have understood the non-doership and non-enjoyership of the supreme self in theory, but it is still a little fuzzy. We need to clearly understand how the supreme self, in its real nature neither acts, nor experiences the results of its actions. To better explain this, Shri Krishna provides an illustration in the next shloka.