The doctrine of divine simplicity has been largely ignored, rejected, or redefined in the last one hundred years of scholarship until the recent resurgence of interest. Specifically, modern apologist theologians and philosophers have largely rejected this doctrine in discussing God’s attributes and the relations of the Trinitarian persons, believing it to be something to apologize for rather than to apologize with. By contrast, a great deal of recent interest in this doctrine has been sparked by James Dolezal, Steven Duby, Matthew Barrett, and others. However, while many have explored and defended the various theological and philosophical issues regarding simplicity, only glimpses of its polemic and apologetic implications have been explored. This paper, which summarizes the main argument of my recent dissertation, argues that a classical understanding of the doctrine of divine simplicity was itself developed and used polemically and apologetically throughout history. Apologists from the early church through the medieval church and into the Reformation explicitly used and depended upon God’s simplicity to support first cause and ontological arguments and arguments to defend the doctrine of the Trinity against cults, heresies, polytheism, and pantheism. This paper will explore a representative survey of important theologians to argue that a classical understanding of simplicity historically served as an essential link in the chain of key arguments for the Christian faith, arguments that many modern apologists still want to use. In other words, without a classical understanding of divine simplicity, classical apologetics fall apart.