Metaphysics is a broad area of study in philosophy that seeks to understand and classify the deepest nature of existence. Most major religions, similarly, attempt to offer an explanation of how and why anything at all, and people in particular, exist in the world. Metaphysics and religion are related, therefore, because religion often attempts to provide a metaphysical understanding of existence. Other questions important to both metaphysics and religion include the nature of the human mind, free will, and the existence and role of God.
The single factor that unifies metaphysics and religion the most is the nature of existence at a fundamental level. A materialist, for instance, holds the metaphysical view that all things can be understood materially without turning to any supernatural forces. Religious believers, on the other hand, tend to believe that the world exists because of a God or gods. A pantheistic view of metaphysics and religion states that there is no real difference between the ideas of "God" and "the world."
Another major issue addressed by both concepts is that of free will. It is not known with scientific certainty whether or not people actually have complete control over their actions and decisions. Metaphysicians seek to study and understand what is meant by "free will" as opposed to determinism and if the two can be reconciled. They also seek to provide rational arguments, sometimes drawing from modern science, for or against free will. Various religions, on the other hand, rely on either free will or determinism as a foundational point in their ethical systems.
Theology is a subsection of philosophy interested in examining God and the divine. As such, it invites contributions from both metaphysics and religion. Important questions in theology include the existence of God, the possibility of knowing God, and the role of God in creating and directing the universe. Some metaphysicians, for instance, argue that there is no God or that the idea of a "god" refers only to an impersonal creator. Religious theologians, on the other hand, often argue for a personal God or for the theological views presented by their specific religions.
How these concepts are studied is based on many different factors, many drawn from philosophy, history, and religion. Some religions, for instance, discourage the questioning of religious doctrines and encourage dogmatic rather than critical metaphysics. Academic philosophers, on the other hand, tend to believe that any questions in metaphysics and religion can and should be studied.