Maximizing on the things you agree on could be useful here. Maybe you wouldn’t want to talk directly about your disbelief in the supernatural (or whatever his specific beliefs/experiences of it entail) but talking about skepticism about other topics like young Earth creationism, the Bible, harmful religious practices, or another related topic that wouldn’t make him feel invalidated would be okay and would give you an opportunity to express your views. Just a thought. I personally think it’s okay to have a topic or two that can’t be entirely shared.
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“Better to reign in Hell than serve in Heaven.” — Satan and TwilightPrincess