I think of that underlying One in immanent terms, a being or life force that dwells within the universe and all its forms, rather than a Creator from beyond who forms a world that is "other" and separate from its own Self.
The ultimate reality is neither immanent nor extra-cosmic but it is the Manifestation or the Cosmos itself.
An immanence would mean that the origin is different from the substance and dynamics of the manifestation/cosmos and so it would mean that this origin somehow created the materials and energies from nothing and then infused the creation to guide it from within.
The origin is the source of the materials as well as of the energy - the materials/energies are its own substance - and as such the origin has partially manifested itself and its manifested substance itself forms the graduated cosmos and guides it functionally through an innate causal mechanism.
The origin which is a unified field of consciousness-energy has various poises - immanent, transcendent and absolute - in its unmanifest as well as manifest state.
The origin in manifestation itself becomes the cosmos.