To nihilists, the only sin is dualism.
We are about reality.
In that sense, God and Nature are one and the same.
Metal has always sounded like church music -- major scales, classical composition, "serious" outlook. It's not unlike Romantic poetry in that respect: it competes with an externalized vision of God, by finding God in everything.
Pantheism, paganism, Hinduism, idealism -- they are all about a single idea, which is that god pervades the world and we are here to fix the organization of the world, not to fight for the individual -- a means -- as an end in itself.
In that sense, metal and any intensely reflected spirituality are the same.
People over 125 IQ points tend to find transcendental idealism in any religion they approach, in every culture, but most concentrated in European and Indian cultures.
Metal is using logic to find this same path.