Final answer:
The subject of this question is Religious Studies, specifically the existence of God and the arguments surrounding it.
Step-by-step explanation:
The subject of this question is Religious Studies, specifically the existence of God and the arguments surrounding it. The question references different philosophers such as John Calvin, Augustine of Hippo, Karl Barth, and Immanuel Kant, who have all contributed to the discussion on the existence of God. The question also mentions Anselm's ontological argument, Descartes' conception of an all-perfect being, and Kant's viewpoint on the limitations of thoughts in establishing existence. These references indicate a focus on philosophical arguments and reasoning in the context of religion.