yadā bhūtapṛthagbhāvam ekasthamanupaśyati | tata eva ca vistāraṁ brahma sampadyate tadā ||13.30||
When one sees clearly, the condition of distinction in the beings, as having its existence in one (ātmān), and from that alone is its projection (distinctions), then he gains Brahman.
In verse 13.27 said the seer is seeing brahman or ātmā remains the same in all being, but some people might think that there are something called ātmā obtain in every being, just like a box of chocolate which got different flavour and shape, but each chocolate for sure is having a whole hazelnut in the centre. It is not like that. This verse clarifies that the distinction is always there in all being - bhūtapṛthagbhāvam, but all bodies, minds, senses are having their being in one ātmā alone. The existence of each one of us is not different from that one ātmā - ekastham, without going through any changes, only names-forms-functions is different. How one ātmā becomes many without going through any change? From one ātmā alone everything here are projected - tata eva ca vistāraṁ. Just like when a lamp is put inside a big pot with different kinds of holes on its belly. Light shines through small holes. It appears many, but it is the same light alone without undergoes any change. In the same manner one ātmā projects as this variety world, where there is no changes on the part of ātmā. Therefore when one can see that subject-object difference is only appearance, there is no real duality, they are just projection, this person is said to be abide in oneself or sometimes referred as has gained brahman - brahma sampadyate tadā.
There is a doubt that if there is only one ātmā which obtains in all being, will ātmā also has limitations of the attributes belong to the beings which is cause by association? It is answered in next verse.
anāditvānnirguṇatvāt paramātmāyamavyayaḥ | śarīrastho’pi kaunteya na karoti na lipyate ||13.31||
Kaunteya (Arjuna)! This limitless self, being beginning-less and without attributes in the body, it does not perform action, and is not affected (by result of action).
A physical body is born, it has a beginning whereas ātmā is without beginning - anāditvāt and therefore does not have the problem inherent in something that begins. And anything which has beginning, it will decline and perish since it is subject to time. When a thing is not subject to time, action can’t be done because action required time. Therefore ātmā doesn’t perform action, thus not affected by the result of action.
Then again, this limitless ātmā has no attributes - nirguṇatvāt. Since there is no attributes, real contact is not possible. When any object which has attributes will change due to the attributes of another object when in conjunction with it. Just like milk has its own attributes, when it is mixed with water which has its own attributes, it becomes diluted. Therefore ātmā being attribute-less doesn’t undergo any change - avyayaḥ. This being so, even though ātmā obtains in the body - śarīrastho’pi, it doesn’t perform action - na karoti and will not be affected by the results of actions - na lipyate. It purposely mentioned ātmā obtained in the body because the body is the place where ātmā can be recognised. Ascertainment of existence of ātmā in the body is to be done first (adhyāropa), then followed by negation of body is not ātmā (apavāda). Ātmā illumines desires, actions and results of actions without being affected at all.
Next verse is the illustration of ātmā being not affected.
yathā sarvagataṁ saukṣmyād ākāśaṁ nopalipyate | sarvatrāvasthito dehe tathātmā nopalipyate ||13.32||
Just as all pervasive space, because it is subtle, is not affected, so too, the self, abiding in all states in the body is not affected.
Space being subtle, means has no form, is not affected by anything that happens in it. When the pot is filled with water, the pot’s space doesn’t get replaced and pushed out of the pot. Only the appearance of empty pot’s space and water are different. It is the same one space where you and I occupy. Being subtle the space doesn’t get affected at all, not to talk about ātmā which is subtler then the subtlest, the basis for all the projections.
To illustrate how one ātmā can illumine all kṣetra, Lord Krsna gives the following verse.
yathā prakāśayatyekaḥ kṛtsnaṁ lokamimaṁ raviḥ | kṣetraṁ kṣetrī tathā kṛtsnaṁ prakāśayati bhārata ||13.33||
Bhārata (Arjuna)! Just like one sun illumines this entire world, so too, the kṣetrī, one who obtains in the kṣetraṁ, illumine the entire kṣetraṁ.
Just like one sun alone illumines the entire solar system, similarly the kṣetrī, one who obtains in the kṣetra, illumines the entire kṣetra. Kṣetrī is ātmā who illumines this body-mind-sense-complex and entire world. There is only one ātmā illumining all this. Anything that we might consider to be a second ātmā is only the ksetra. When we count another person what we are really counting is only the body or the mind, they are kṣetra, not ātmā. All ksetra are projection of one ātmā alone.