What matters most are things like people, love, understanding, courage, friendship, beauty, etc. According to many contemporary metaphysicians, what is most fundamental are things like sets, points, photons, charge, spin, the electromagnetic field, etc. It's almost as if the metaphysicians took the fact that something matters to be evidence that it isn't fundamental.
But here is a plausible hypothesis or at least heuristic:
- Fundamental predicates apply primarily to fundamental entities, and derivatively to other entities.
Thus, either persons will be themselves fundamental, and primary bearers of value, or else persons will be partly constituted by something fundamental which is a primary bearer of value. The best candidate for this valuable constituent is the soul. Hence, either persons are fundamental or they have souls that are fundamental.
In fact, I would conjecture that we should turn on its head the correlation between fundamentality and not mattering that we find in much contemporary metaphysics. The more something matters, the more reason we have to think it is fundamental, I suspect. This may lead to a metaphysics on which there are fundamental facts about persons, their psychology and their biology, a realist metaphysics with a human face.