If we look at life using only our 5 physical senses combined with our intellect terms such as “God” or “ground of being” become effectively meaningless. If there is no reality beyond the physical then terms such as "being" only refer to physical beings, not to any other kind of living entity that may exist in another realm or reality beyond the physical. In the case of a God, if we cannot communicate with or sense such an entity then they may as well not exist.
The person who holds the belief that the physically universe is the only one that can be experienced or observed cannot be aware of non-physical entities and therefore must treat them as if they don’t exist. For others who have experiences that go beyond the materialist worldview the possibility of being aware of and communicating with non-physical entities may be seen as entirely possibility. In this case the idea of a reality that lies unseen but yet can be experienced by the usually physically focused consciousness is seen as a possibility. Therefore the notion of a non-physical God/source of being is seen as a possible reality rather than an imaginary notion as materialists must see it.