"Entities should not be multiplied beyond necessity." Occam's Razor? Somehow I fail to see the correlation.
This is often paraphrased as "All things being equal, the simplest solution tends to be the best one." In other words, when multiple competing theories are equal in other respects, the principle recommends selecting the theory that introduces the fewest assumptions and postulates the fewest hypothetical entities. It is in this sense that Occam's razor is usually understood.
We know the natural exists. We don't know the supernatural exists. In fact, we can't even properly define supernatural or spiritual essence seeing that we don't know it exists, cannot detect it in any way, and therefore have no way of deducing and declaring what it is.
And when you also take into account all the myriad of other variables that would result in the acceptance of a spiritual reality, it seems to be a far better, less involved, simpler way to explain phenomena if we keep to what we know exists (or what we have reason to assume exists, i.e. by a mathematical necessity) and don't try to use explanations involving things that may for all we know exist nowhere else but in our heads.