One of the debates that has swirled around Constantine the Great is the issue of whether he was a genuine Christian. One theory is that he was an exponent of Realpolitik. He remained a pagan, but exploited the Christian church and elements of Christian doctrine to exert his control over rivals who served pagan gods. In this view, Constantine was leveraging off the Christian God to claim authority for his rule, his precepts, and his control. He was never a genuine believer. At best he was a cynical manipulator.
Another theory is that Constantine was a genuine Christian, which is to say he was two shades away from a credulous superstitious simpleton, since all Christians alike are to be thus characterised.
In his book, Defending Constantine: The Twilight of and Empire and the Dawn of Christendom (Downers Grove, Illinois: IVP Academic, 2010), Peter Leithart gives careful consideration to this question.
Naturally, Constantine cannot be separated from the world view in which he lived and served. It was a pagan culture in which he was raised. Moreover, Constantine as emperor over a diverse empire often used argumentation and appeals which would have been meaningful to his pagan subjects and subordinate civil and military authorities. Thirdly, Constantine, like all Christians, would have had residual pagan beliefs, doctrines, and principles in his heart, which--as with all of us--would require gradual rooting out over time. "I used to think xxx, but now I have come to understand . . . ," is a frequent, repeated refrain of ordinary Christians.
Moreover, it is all too easy to be guilty of anachronistic thinking in expecting that ancient Christians could draw upon the collected corpus of teaching wrought by the Holy Spirit as He has instructed the Church over two thousand years. If Constantine did not understand the doctrine of justification by faith as declared in the great confessional documents of the Reformation, why would that surprise us? To require that he did as a test of the genuineness of his faith is silly.
One thing is clear. Constantine had rejected the pagan gods. He clearly believed that there was one true God. He did not shy away from sharp polemical utterance against paganism. In many ways, Constantine appears to have understood this far better than many modern Christians. It was one of the key theological battle grounds of his day. Against all the traditional gods of his age and culture, Constantine took his stand. And he stood firmly upon the teaching and revelation of Scripture.
One criticism of Constantine's faith is that while he spoke often of the Most High God, there are few extant references in his writings to the Lord Jesus Christ. Therefore, at best, some argue, he should be considered a proto-Deist, rather than a Christian. Once again, this is just silly and facile. Leithart skewers this in the following way:
In one sense, it is hardly surprising that we find comparatively few explicit references to Jesus in Constantine's writings. So far as we know, he did not keep a spiritual journal, not did he write hymns or mystical poetry. Most of the writing we have from Constantine's own hand consists of official correspondence with subordinate civil rulers or bishops, a genre not known for pious flourishes. Given the nature of most of the extant writing of Constantine, the striking thing is how often he turns to theological, and frequently specifically Christian, themes. I dare say that one will find more frequent references to Christ in Constantine's official pronouncements than one could find in the Federalist Papers. (Ibid., p.88.)Touche. In fact the one extant sermon we have from Constantine is filled with references to the Son of God, the Christ, the Saviour and His central place in human history. Whilst we have only one such address extant, we are also told that Constantine constantly gave homilies and religious addressed to his courtiers, so much so that his palace was said to have virtually turned into a temple.
Leithart's summary statement on the issue of Constantine's faith runs thus:
. . . the Constantine we are examining was a Christian. Flawed, no doubt; sometimes inconsistent with his stated ethic, certainly; an infant in faith. Yet a Christian. (Ibid., p.96.)This is fair and consistent with the evidence we have available. It is the most probable position by a country mile. All contrary views would make Constantine a cynical, depraved kind of fellow. Take your pick.