In The Divine Relativity, Charles Hartshorne’s concern is with the question “What can most reasonably be meant by the religious word God?” He thinks that classical theism—the monotheism developed and defended by such philosophers and theologians such as Saint Augustine, Saint Thomas Aquinas, Moses Maimonides, and Avicenna, and influenced significantly by Plato, Aristotle, and Plotinus—is as much Greek as Jewish, Christian, or Islamic. He also regards classical theism as an incorrect restatement of the central religious concepts—particularly the concept of God—as philosophical categories, and he endeavors to show that his assessment is correct.
His concern is also to offer a restatement of the central monotheistic concepts, one cast in process philosophy rather than substance philosophy terms. A substance is something that has properties, is not itself a property, endures through time, and retains its identity over time, despite change of its nonessential properties. A process, for a substance philosophy, is simply a matter of a substance gaining a property it lacked or losing a property it had. For Hartshorne, there are processes, but not substances; he takes a process (not, of course, as defined by substance philosophy) to be the basic sort of entity, of which everything else, God included, is made. He takes his restatement to be a significant move toward making philosophical theism accord well with contemporary natural science, theology, and philosophy.