I do not think there is any demonstration properly so called of the existence of the Supreme Being independent of matter.
Animism is the creed that God is in nature; and Voltaire’s profession of it helps us to understand the history and reasoning behind Thomas Jefferson’s own profession of it:
To talk of immaterial existences, is to talk of nothings. To say that the human soul, angels, God, are immaterial, is to say, they are nothings, or that there is no God, no angels, no soul. … Jesus taught nothing of it. He told us, indeed, that ‘God is a spirit,’ but he has not defined what a spirit is, nor said that it is not matter. And the antient fathers generally, of the three first centuries, held it to be matter, light and thin, indeed, an etherial gas; but still matter.
There is much that has been forgotten about the religion of the leaders of the age of the enlightenment, and so let us end this short remembrance with the joy and confidence we gain by reading these proofs that Voltaire and Jefferson were animists, who believed God and nature are indistinguishable.