If one is able to develop a fully worked out explanation for :-
1) How matter-energy-forces-space-time are integrated with each other
2) How and why they interact with mathematical regularity in accordance to the laws of physics
3) How does logical/mathematical/informational domains interact with physical domains
4) How and why the physical domain is so arranged that emergence of complex wholes become possible
5) How knowledge and consciousness is explained and how they interact with (1)-(4)
In terms of a single integrated well-validated theory, then nothing else needs to be explained. If, suppose, this theory posits an ur-entity like Brahman with certain features that explains and predicts the features above with precision, then, the justification for believing its existence is the success it has in explaining and predicting all these features of the world, which currently nothing can. Then saying, by this entity and not something else, is because, it and only it has shown itself able to provide these explanations and predictions and nothing else has.