Christoph Markschies begins his book Christian Theology and Its Institutions in the Early Roman Empire: Prolegomena to a History of Early Christian Theology by defining the terms ‘theology’ and ‘institution’, which is a very good place to start. He notes that in the second and third centuries, “theologians” were the likes of Opheus, Homer, Hesiod or “certain cultic functionaries” (6); that is, poets and priests. It wasn’t until later that theology or theologian became a term for some sort of rational explication of a beliefs, and Markshies highlights the importance of Justin Martyr, Clement of Alexandria, and especially Eusebius of Caesarea in this regard. But behind them, of course, stands Plato.
Plato not only discovered the word that came to designate Christin ‘theology’ from the high middles ages; his philosophy also in a sense first made possible the elaborate Christian “theology” of the imperial period and thereby basically paved the way for the close association between Platonic philosophy and Christian “theology” that characterized Christian antiquity (admittedly with varying degrees of intensity). Even if the word θεολογία was initially not used in this way in antiquity itself, the relatively quick development of ‘theology’ in ancient Christianity presupposes a good bit of that bold metaphysical certainty with which Plato, in precisely that passage in which the word θεολογία first appears, also asserted the possibility of ‘theology’ as an ‘appropriate representation’ of God. No Christian ‘theology’ could have been developed in antiquity on the basis of a skeptical approach, like the viewpoint favored by the Platonic Academy for many years after the metaphysical certainty of Plato was broken in skepticism beginning in the second century BCE. Rather, the simplifying standardization as well as the popularizing ‘theologization’ of the various antiskeptical philosophical directions int he early Roman Empire, which followed as a reaction to skepticism, were an important presupposition for the emergence of Christian ‘theology.’
(Christoph Markschies, Christian Theology and Its Institutions in the Early Roman Empire: Prolegomena to a History of Early Christian Theology, trans by Wayne Coppins [Waco, TX: Baylor University Press/Mohr Siebeck, 2015] 12–13).
This analysis by Markschies coheres well with George Karamanolis argument in The Philosophy of Early Christianity, where he argues for the importance of responding to skeptical arguments as the impetus to Christian theological development (or, put another way, the rise of Christianity as a philosophical school in its own right). If answering skepticism is important early on, it would be interesting to compare later Christian responses to skepticism.