"Foundations" are propositional facts that are either self-evident or borrowed from other sciences, and which serve to explain and verify issues related to a specific science. In this case, there are "ontological foundations" or theological principles—in both a general and specific sense—that play a key role in explaining and verifying Mahdian doctrine. Some of these ontological bases comprise the law of causality, monotheism, divine decree and predestination, divine wisdom, both legislative and existential guidance, finality, leadership, and the jurist's authority. This paper takes a descriptive-analytical approach in examining how these foundations play a crucial role in interpreting and explaining Mahdian doctrines. It concludes that the legitimacy of the Mahdian society and the actualization of its fundamentals—most importantly those related to defense, security, and warfare strategies—are all contingent on divine approval and commandments, in addition to adherence to basic knowledge and the dictates of the Sacred Religion of Islam.