Whitman absorbed deist principles from his father; he was equally influenced by his mother’s Quaker background. He embraced the Quaker emphasis on individual experience of the divine — what Friends call the “inner light” — as well as the concept of “that of God” existing within every person. Whitman’s poetry reflects Quakers’ radically egalitarian theology

https://www.churchtimes.co.uk/articles/2019/31-may/features/features/walt-whitman-a-prophet-found-under-your-boot-soles