Irenaeus (c. AD 130–202)
Some might express surprise at the choice of Irenaeus. He is best known for writing Against Heresies, a work that relentlessly dismantles early Gnosticism. Granted, the first two books of this lengthy work are often tedious because they recount and describe all the various gnostic myths and errors. Sadly, however, many readers have failed to reach books 3–5 because they gave up before getting to these sections of the works. James Payton has done every student of the early church a favor by editing a condensed version of Against Heresies under the title Irenaeus on the Christian Faith. This work allows readers to focus on books 3–5, where Irenaeus provides a positive exposition of Christian teaching.
Athanasius (c. AD 296–373)
Athanasius is one of the most significant fathers of the early church, primarily because of his contribution to the Trinitarian debates and his refutation of various forms of Arianism. His defense of orthodoxy led to his being exiled multiple times. Athanasius wrote numerous works. The best entry into his writing is likely the pair of works titled Contra Gentes and De Incarnatione (Against the pagans and On the incarnation). In the first work, Athanasius critiques the pagan religions, and then in the second work he defends the necessity and nature of the incarnation of Christ.
Gregory of Nazianzus (c. AD 329–90)
Gregory of Nazianzus was a key figure in the resolution of the fourth-century Trinitarian controversies. His style of writing is extraordinarily beautiful, especially when his reflections on the Holy Trinity result in lengthy doxologies. Much of his best writing is found in his numerous orations. A good starting place is his five theological orations on the Trinity. They are now available in a small volume titled On God and Christ.
Augustine (AD 354–430)
Augustine is widely acknowledged as the greatest theological mind of the first thousand years of the church’s history. His influence continues to be felt to this day, so his significance cannot be overstated. Augustine’s written output was extraordinary, so knowing where to begin with him is almost as big a challenge as knowing where to begin with the church fathers themselves. It is probably impossible to go astray, however, if one begins with his Confessions. This work is more than a mere autobiography. It is also a work of profound theology. Though it is not a primary source, I would be remiss if I did not also recommend Peter Brown’s biography of Augustine. This work remains the best biography of anyone, ancient or modern, that I have ever read.
Cyril of Alexandria (AD 378–444)
Of these five church fathers, Cyril of Alexandria is the one with whom Protestants are likely the least familiar. This should not be the case, for Cyril was just as significant in the Christological controversies of the fifth century as Athanasius and Gregory were in the fourth-century Trinitarian controversies and as Augustine was in the fifth-century Pelagian controversy. Cyril’s theological works, in fact, set the parameters for the Chalcedonian settlement, and his doctrine is enshrined in the Definition of Chalcedon. The best introduction to Cyril, including a lengthy selection of his most important primary sources, is John McGuckin’s book Saint Cyril of Alexandria and the Christological Controversy.
There are certainly other early church fathers whose writings are significant and fascinating, and many different titles could be suggested. These five individuals are a good place to start, however, so take the time to make their acquaintance. Tolle lege: Take up and read.