It's hard to define naturalism. After all, even if there were souls and the like, naturalists could still treat them as natural phenomena.
Maybe a better way to characterize naturalism is that it is the view that objectively speaking in itself there is nothing numinous: Nothing holy or sacred, but only the good or right; nothing sinful or unholy, but only the morally wrong; nothing uncanny or eldritch, but only the unusual or the scary; nothing aweful, but only the impressive; nothing mysterious, but only the puzzling or the strange; nothing fascinating, but only the attractive; nothing sublime, but only the beautiful.
Some naturalists will have an error theory about the holy, sacred, sinful, unholy, uncanny, eldritch, aweful, mysterious and fascinating. Others will say that such that such predicates can be rightly applied, but they indicate in large part our attitudes to these things, rather than indicating the intrinsic characteristics of things that make those attitudes appropriate.
(It is also interesting that even some of the de-sacralized replacements—especially the good, the right, the wrong and the beautiful—are troubling to many naturalists.)