Origen was an ex post facto heretic, anathematised by the second council of Constantinople in 553, some three centuries after his death.

Alexandria, Origen's birthplace, was the intellectual center of the Hellenistic world and a hotbed of speculative Platonic philosophy. In the first century Philo of Alexandria had, through his biblical exegesis, attempted to fuse Platonism and Judaism. Origen, with greater success, sought to merge Christianity with Greek philosophy.

It was however Origen's Platonism that did him in. Following Plato, he subscribed to the doctrine of pre-existent souls, which was not acceptable according to the orthodox industry standard that was later established. On Origen's account, God's first creation, before time, was a collectivity of souls. Of these, all but one, the human soul of Christ, fell away. In the end, however, all humans and every spirit, even the devil, would be saved, returning to a state of "pure mind".

Reading this one asks: where is it all coming from – the hierarchy of incorporeal, conscious beings, the precosmic fall, the apotheosis of all souls at the end of time? There is no argument for this grand cosmological story. The only argument is in the elaboration of metaphysical machinery through which it is articulated. But one could say the same for other Hellenistic philosophers, including Origen's contemporary Plotinus – a fellow student of the ur-Neoplatonist Ammonias Saccus. Origen was on the cutting edge of Hellenistic philosophy, characterised by speculative metaphysics, mysticism and plain flakiness.

Origen was also on the cutting edge of biblical scholarship as the first Christian theologian to learn Hebrew in order to read the Hebrew Bible. Like Philo, Origen read scripture allegorically. The Bible was divinely inspired, he held, but since so many of the stories in the Bible were clearly false and even ridiculous, God's intention must have been that they not be taken literally.

"What intelligent person", Origen asked, "can imagine that there was a first "day", then a second and a third "day" – evening and morning – without the sun, the moon, and the stars … Who is foolish enough to believe that, like a human gardener, God planted a garden in Eden … I cannot imagine that anyone will doubt that these details point symbolically to spiritual meanings, by using an historical narrative which did not literally happen."

Origen's theology was always controversial, but it has always been controversial whether Origen should be regarded as a heretic. Impeccably orthodox theologians admired him. Saints Basil and Gregory of Nazianzus collected his works as the Philocalia of Origen and promulgated them; St Jerome translated over 80 of his sermons for the edification of western readers deficient in Greek.

During his lifetime, Origen's orthodoxy was never questioned and even later the chief bone of contention was his doctrine of the pre-existence of souls – including the human soul of Christ. His fanciful interpretations of the Bible were no worry, biblical literalism being a modern invention. Even his doctrine of universal salvation was not clearly unacceptable. The emperor Justinian, an avid amateur theologian keen on eternal damnation, pressed the second council of Constantinople to condemn this doctrine, but the bishops did not ratify his proposal: St Clement of Alexandria and St Gregory of Nyssa, both known universalists, survived with their sanctity intact.

It's hard to imagine what Origen, or his orthodox contemporaries, would make of contemporary Christianity. I suspect they would find the conservative evangelical variety unintelligible and would even be puzzled by "mainline" Christianity. Why, they'd wonder, were these third millennium Christians so utterly indifferent to vital metaphysical questions? Why did they care about the historical accuracy of biblical narratives? Why were they so interested in stories about the human Jesus and so little concerned about the metaphysics of the logos, which became incarnate? Why was their Christianity so simplistic, prosaic, anti-intellectual and deadly dull?

I got religion as an undergraduate, reading church history and the Greek fathers of the church. I was taken by the romance of late antiquity in the east, fantasising a world where metaphysics and mysticism were popular pastimes, where, as Gregory of Nyssa reports, shopkeepers and laborers argued fine points of theology in the streets. If I had been brought up with the puerile, prosaic religion of Sunday school Jesus-stories, church rummage sales, happy-clappy services and self-help programs, dull sentimentalities and dull moralism – I would never have given Christianity a shake.