Simply another excellent book by Charles Freeman. Though "just" an independent historian, not an academic (though he has taught International Baccalaureate classes and the British version of continuing education classes) in history, let alone an academic in theology, he has a sure grasp of both areas, just as he did in Closing of the Western Mind, also five-starred here.
Freeman's thesis is that, unlike Constantine with the Council of Nicaea, Theodosius I had a predetermined result before calling the Council of Constantinople, which essentially gave us what many Christians today call the "Nicene Creed." (Constantinople expanded broadly on the original document, at Thodosius' direction.)
Theodosius, as Eastern Emperor (and at end of life, the last man to, at least on paper, reunite the empire), was determined that the Nicene creed, lowercase — Homoousian, NOT HomoIousian, as in Arians and other subordinationists need not apply — would be the Christianity of the empire, period and end of story. Along with this, he moved far beyond both Constantine and Constantius in an illiberal direction. Freeman argues that it was his imperium, even though philosophical academies remained open for decades, that saw the installation of the first version of doctrinaire Christianity.
However, he also notes that Constantinople's creed caused new problems, even with it in a broader form than Theodosius wanted. Namely, it brought the issues of Jesus' "two natures" to the forefront.
As I was transitioning out of my long-ago conservative Lutheranism, I never really thought about how silly traditional Christian theology sounded in trying to claim Jesus said, did or felt X "according to his human nature" and Y "according to his divine nature." But that's exactly what Gregory of Naziansus did long before it was adopted in the West. And it is silly. Period.
Speaking of "the West," Freeman also shows how popes had basically no effect on any of the seven ecumenical councils. Through the first four, Christianity was still much smaller in the Roman West than East, especially in Gaul and Britain, first. Second, although popes themselves still spoke Greek in this period, and with some level of fluency, the average parish priest or even bishop in Italy, let alone to the west, did not.
Freeman details this with Augustine. He gives him a separate chapter for the post-Constantinople "resurrection" of Paul, especially the Paul of Romans, and its baleful influence on most later Western Christianity. He does miss a small beat here. Orthodoxy, even more than focusing on other parts of Paul, has long looked to Johannine theology and soteriology as its guiding light.
Concluding chapters take the Theodosius-inspired illiberality up to the Trecento and the first dawn light of the Renaissance. This is arguably counter-revisionist history versus the past few decades that have seen many historians, both religious and not, claim the "Dark Ages" weren't. In his native Britain, especially, but also in spots on the Continent, by looking at the great dropoff in manufacturing, loss of technology (Rome invented Portland cement, then the method for making it was lost for a millennium, though that's not one of Freeman's examples), and the minuscule size of bishops' and monasteries' libraries, Freeman makes a good case that these centuries were in many cases dark indeed.
A Bart Ehrman, who, while claiming to be an agnostic, is probably still a seeker at heart, would do well to read books like this before writing any more about the semi-miraculous rise of Christianity.