All Religions are One presents William Blake’s argument that human beings share a common spiritual and imaginative faculty, which he calls the Poetic Genius. He describes this faculty as the essential human reality from which outward forms, thought and expression arise. Although individuals differ, Blake maintains that the same underlying capacity is present in everyone.

Across seven principles, Blake extends this idea to philosophy and religion. He argues that different philosophical systems reflect individual expressions of the Poetic Genius, while the religions of different nations develop from varying receptions of this universal source. He identifies the Spirit of Prophecy with the Poetic Genius and treats the Jewish and Christian scriptures as particular expressions of it.

The work concludes that religions can be infinitely varied while sharing a common origin. Blake therefore presents religious diversity not as evidence of entirely separate spiritual sources, but as different manifestations of a universal human imaginative principle.