Osborn points out that "at the end of the first century Christianity did not count, yet at the end of the fourth century it reigned supreme and other religions did not count" (p 9). A shocking reversal, and a growth in theology was one reason for the spread of Christianity. Osborn concludes that "linking the Bible and philosophy" (p 127) was the one step that set Christianity on some of its firmest intellectual grounds.
The growth in theological arguments was due to the spread of heretics that the Christians needed to refute, as well as questions brought to them by other Christians. In the second century, Christianity faced Marcion and his abridged Gospels, and the Gnostics, who were always multiplying and forming new groups. Gnostics had no theological arguments, and a bewildering, synergistic jumble of beliefs, not too mention an ever increasing number of aeons. Irenaeus "showed that Gnostic myths were inappropriate and genuinely funny" (p 15).
In addition, Jews had ejected Christians from their synagogues by various curses, yet there appear to have been a number of Jewish Christian groups, although information on them is scanty and confusing.
Justin, Clement, and Irenaeus were among the most noted Christian theologians. They felt free to use whatever Greek philosophical arguments they could. Platonism and Stoicism were both highly regarded by the elite in the Greco Roman world, so pointing out wherever Christian beliefs coincided added a gloss to their arguments.
Clement made use of Philo and Plato. Plato had asked if there was a first principle, which sounded to many Christians like a definite reference to God. The ancient Greeks had sought to find the way to live, and Clement argued that the way to live was in the light of God's truths.
Christian theologians used "two methods of handling scripture. The first was through symbol or allegory and was directed chiefly to the Old Testament" (p 69) and the other was through logic. Justin's proofs against Trypho were found in the prophecies found in the Old Testament.
Monotheism and a real, historical Jesus proved to be flash points in a pagan society with its vast circus of gods. Clement point out that "Marcion starts with two gods and finishes with nine...Valentinus started with two...and finishes with a brood of thirty aeons...Marcion's strange God is still more incredible because he has caused no world which might prove his existence" (pp 120-1).