Question: What is the difference between Brahman and Ishwara?
Brahman is nirguna formless and unconditional, – no upadhi (no conditioning). Brahman appears as Ishvara due to Maya upadhi. Brahman in the role of creation is called Ishwara. Brahman as Ishwara is the cause (nimitta karana) for the appearance of Universe. Universe can be manifest or unmanifest.
Brahman with unmanifest universe or creation is called Ishwara. When the ideas (creation in unmanifest mode) take shape, Brahman appears as Ishwara. Ideas have not yet manifested (in causal form). Universe can be manifest or unmanifest in Ishwara. Brahman with Maya Upadhi is called Ishwara, where Maya has still not appeared. Maya is called avyakta – unmanifest form of Universe.
Manifest form of universe is called Prakriti. Ishwara is Brahman with unmanifest Maya. Unmanifest prakriti or nature is called Maya.