The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
32. But (Brahman is called a bank &c.) on account of (a certain) equality.
The word 'but' is meant to set aside the previously established conclusion.--There can exist nothing different from Brahman, since we are unable to observe a proof for such existence. That all existences which have a beginning spring from, subsist through, and return into Brahman we have already ascertained, and have shown that the effect is non-different from the cause.--Nor can there exist, apart from Brahman, something which has no beginning, since scripture affirms that 'Being only this was
in the beginning, one, without a second.' The promise moreover that through the cognition of one thing everything will be known, renders it impossible that there should exist anything different from Brahman.--But does not the fact that the Self is called a bank, &c. indicate that there exists something beyond the Self?--No, we reply; the passages quoted by the pûrvapakshin have no power to prove his conclusion. For the text only says that the Self is a bank, not that there is something beyond it. Nor are we entitled to assume the existence of some such thing, merely to the end of accounting for the Self being called a bank; for the simple assumption of something unknown is a mere piece of arbitrariness. If, moreover, the mere fact of the Self being called a bank implied the existence of something beyond it, as in the case of an ordinary bank, we should also be compelled to conclude that the Self is made of earth and stones; which would run counter to the scriptural doctrine that the Self is not something produced.--The proper explanation is that the Self is called a bank because it resembles a bank in a certain respect; as a bank dams back the water and marks the boundary of contiguous fields, so the Self supports the world and its boundaries. The Self is thus glorified by the name of bank because it resembles one.--In the clause quoted above, 'having passed that bank,' the verb 'to pass' cannot be taken in the sense of 'going beyond,' but must rather mean 'to reach fully.' In the same way we say of a student, 'he has passed the science of grammar,' meaning thereby that he has fully mastered it.
176:1 Which would be unnecessary if the two were not distinct.