Verse 2.3.13

अस्तीत्येवोपलब्धव्यस्तत्त्वभावेन चोभयोः ।
अस्तीत्येवोपलब्धस्य तत्त्वभावः प्रसीदति ॥ १३ ॥

astītyevopalabdhavyastattvabhāvena cobhayoḥ |
astītyevopalabdhasya tattvabhāvaḥ prasīdati || 13 ||

13. He should be known to exist and also as he really is. Of these two, to him who knows him to exist, his real nature becomes revealed.

Shankara’s Commentary:

Com.—Therefore, having abandoned the theory of those who argue for non-existence, the atman should be known as existing, as productive of effects and conditioned by intelligence. But when the atman is devoid of that and subject to no modification (an effect has no existence independent of the cause); as the sruti says ‘a modification is a mere matter of speech and name; that it is mud is alone true,’ then, is the true nature of the atman unconditioned, devoid of indicative marks, and incapable of being thought of, as existent or non-existent. In that nature also, ‘the atman should be known’ follows. Of these two] of the conditioned and the unconditioned, i.e., known as existence and its true nature; the genitive case has the froce of Nirdharana, i.e., determining; of the atman previously known as merely existent] of the atman known by the belief in its existence produced by its limitations, i.e., its perceived effects. Afterwards, the real nature of the atman subject to no condition, different from both the known and the unknown, i.e., the manifested universe and the prakriti, one without a second, and indicated by the srutis ‘ not this, not that, etc.,’ ‘not gross, not subtle, not short ‘in the invisible, bodiless, supportless, etc.,’ faces him who had previously realised it as existent.