Well, so the story goes, if G.d is the author of all of reality then the human experience is known to Him. And by enter, it would be perfection entering imperfection. A spiritual state entering a physical state. The unknowable becoming knowable, pure abstraction becoming subjected to simplification and objectiveness.
The anthropomorphic god is a human construct.
As for G.d and physical reality, once again as the story goes, we each at birth are conjoined with a spirit which is of the same substance as G.d. This is not an aspect of physical reality, but it is effected by how we have lived our lives.
Each level of existence somewhat understands the levels below, but not above. As humans we can understand, animal, vegetable and mineral. As the story goes, G.d need not enter below to know all the levels below.
