Reflections on Brahma-Sutra-Bhasya II.i.9:
When we speak of material cause and effect in the classical examples of clay and vessels or gold and chains, rings etc made of gold we need to distinguish between the different senses of cause and effect that are used in sentences such as - The fungus on your bathroom wall is caused by condensation or smoking cause lung cancer and so forth. In the one you have matter taking different forms but viewed simply as matter it remains unchanged. There is no question of their being a reversal of effect back into cause, matter will always have a certain form even it is not conventionally recognised as such. Effects in the other cases such as condensation causing fungus remain as an advancement of a situation, there is a temporal aspect which is irreversible.
There is an analogical connection between the different examples of cause and effect but none of them in my view is the central paradigmatic case. Vedanta seems to make material cause/effect the paradigmatic one particularly in relation to cosmological speculation. However a hedging locution is employed when cause and effect are said to be non-different. They are claiming ground between the ‘same’ or ‘identical’ and ‘different’ or ‘separate’.
You could say that this is a monist view to be contrasted with the setting in motion of a Cosmos by a creative act. But when you consider the Doctrine of Divine Conservation the intimate connection between pure being and contingent being swings back towards non-difference.
Shankaracarya in his commentary on the Chandogya Upanishad proposes the idea that form is true in name only (i.e. this is a cup, pot etc), the reality is the clay itself which is unchanging. Here in the B.S.B. he offers the distinction between creation and creator as a mere appearance due to superimposition/adhyasa:
The way that the objection has to be met there (during continuance/creation) by holding that the cause is not affected by the product and its characteristics, these being superimposed on the cause by nescience, is equally to be followed in the case of dissolution as well.
How Nescience/Avidya (personal) or Maya (cosmic) ignorance arises is an interesting question that divides advaitins. In the right hand corner Tula Avidya and in the left hand corner Mula Avidya. That is a topic for another post.
In this commentary on B.S.B. II.i.9 Shankaracarya is more interested in the concept of absorption when the cosmos is reabsorbed into absolute pure being in the mode of pralaya. For the reasons given he holds that there is no difference in it. Resorption itself would be an impossibility if the effect should persist in the cause together with its peculiarities.
That brings him to consider personal experiences of absorption. We drop from the personal state of dreaming into deep sleep and our personal consciousness becomes impersonal and undifferentiated. The yogi in meditation can have a conscious experience of this absorption. What Shankaracarya has to say about this runs counter to the goal of yogic practice.
As in natural slumber and samadhi (absortion in divine consciousness), though there is a natural eradication of differences, still owing to the persistence of the unreal nescience, differences occur over again when one wakes up, similarly it can also happen here.
If samadhi is not realisation, what is? Only knowledge can eradicate ignorance. We must somehow come to know that we always are what we are and spinach doesn't help.