In the face of persecution, ignorance, and hostility, the Church needed to provide a stout defence of its practice and beliefs. The writers who provided this defense are sometimes referred to as the apologists (meaning those who explain or defend their beliefs, rather than apologize). Their aim was to provide a rational explanation to people more acquainted with Greek philosophy and to persuade the Jews to accept Jesus as their Messiah.

Among the earliest apologists were Aristides and Quadratus, who wrote to the emperor Trajan offering a rational explanation of their beliefs. More famous is Justin Martyr, who taught Christian philosophy in Rome in the 140s and 150s and worked to express Christian doctrines in philosophical terms. Justin was aware of the outlandish accusations leveled against the Christians by pagans, such as illicit sexual relations and cannibalism. He refuted these in his two “Apologies,” and defended the Christians against the charge of offending the gods and of not being true patriots. The fact that he could address the emperor and the senate shows the important position Christians were assuming within the empire a little over a century after the lifetime of Christ.

Perhaps the most poetic of early apologists was the unknown author of the Epistle to Diognetus, which was probably written in the late second century to explain the Christian religion to an interested pagan. “Christians,” the author writes, “are not distinguishable from other people, neither by origin, by language nor by mode of dress. They do not live in their own cities, nor do they have their own language, nor indeed do they live any special style of life. They live in their own countries, but as foreigners; every foreign land is their homeland, and their homeland is as a foreign country. They live their lives on earth, but are citizens of heaven. They obey the laws of the land, but by the tenor of their lives, they live above the law. They love everyone, but are persecuted by all. They are unknown and condemned; they are put to death and gain life. They are poor and yet make many rich. They are dishonored, and yet gain glory through dishonor. They are attacked by Jews as aliens, and are persecuted by Greeks; yet those who hate them cannot give any reason for their hostility. To put it simply, the soul is to the body as Christians are to the world … The soul is in the body but is not of the body; Christians are in the world but not of the world.”

Several of the apologists were also important Church leaders and theologians. Irenaeus (140–202) was the second bishop of Lyons, in the south of Gaul (modern-day France). An energetic opponent of Gnosticism and various other heresies, he wrote extensively, his most important work being the hugely influential five-volume Against the Heresies. Irenaeus was also an important theologian, who worked to clarify the canon of the New Testament and whose Presentation of the Apostolic Preaching became a standard work.

He sought to clarify what was truth and what was error by appealing to and trying to define “the Rule of Faith,” the basic core of Christian faith, as a rule by which the truth or otherwise of heretical and orthodox teaching could be judged. This core of faith was eventually to be summarized in the great creeds of the fourth century.

Irenaeus and most of his fellow apologists sought to place Christianity right at the heart of contemporary culture. In so doing, they assimilated many philosophical and cultural elements of Greco-Roman civilization. They were largely pragmatic and embraced the attitude of adapt and adopt: pagan festivals were taken over to become Christmas and Easter, and a place was found for pagan philosophy and literature in Christian thought, as a preparation for the gospel. When pagans argued that Christianity would weaken the State, the apologists countered that, rather, it would strengthen the State against the immorality that attacked it.

Some objected that in adopting so much of Greco-Roman culture, Christians were also taking on its flaws. Tertullian, in particular, opposed the marriage of Greek philosophy and Christian theology, saying “What has Athens to do with Jerusalem?” Rather than giving rational explanations of his faith, he preferred to say, “I believe because it is absurd.” His was a lone voice. The apologists’ adoption of philosophy was effective and it was to dominate the future. Christian theology was increasingly to be expressed in philosophical terms – as it still very often is today.

Although the apologists’ writings failed ultimately to convert the Roman world to Christianity, they nevertheless offered a sober defense against the sometimes hysterical attacks of their enemies, and contributed in no small way to the Church’s developing understanding of Christian doctrine.