He his arguing against property nominalism, and for a notion of universals. That is, he is arguing that properties are more than their particular instantiations; that there is some universal form present in all things with the same property.
This is a controversial point of view in philosophy, but no more controversial than any other point of view ... :wink: ... it is one that I myself share.
But it is perfectly compatible with a naturalist program. Indeed, many of the most famous people who argue for universals are themselves fervent naturalists. I am thinking in particular of the philosophers David Armstrong and David Lewis, among others.
So what he’s arguing may be true, but it is entirely irrelevant to theism.