In the second chapter of De Incarnatione Verbi Dei St. Athanasius, while offering a positive account of the metaphysics of incarnation and redemption, also implicitly develops a grid for examining other religions and their claims to provide an avenue of redemption.
The Incarnation is rooted in two things, which, according to Athanasius, must happen for true redemption to occur. Because the fall consists in both an offense and a corruption, there must be both propitiation of the transgression and a restoration of nature. Athanasius asserts that, while any deity could pardon the offense by fiat, only an incarnate divinity could take on the task of restoring nature. The incarnate divinity must necessarily be the Creator of the race as well; what was created free from corruption must be redeemed from its corruption by the one who established it in the first place.
If we allow that a deity could, by fiat, establish some kind of redemption based on observances and works, there remains the nasty problem of the corruption of nature. Such a fiat would be an eternal and transcendent decree, and it is hard to imagine, without pointing fingers, how a religion based on this kind of redemption would look. But it also brings to mind a dilemma: either there is a corrupted human nature which requires some kind of divine action in the immanent realm, or, if there is no corrupt nature that requires such an action, there is a problem of explaining why sin occurs at all, let alone at the scope it does.
I’m interested in knowing whether this little treatise was preserved in the West at all. According to Jaroslav Pelikan, during the 10th and 11th centuries, theologians realized they could not address the issue of predestination without first understanding the person and work of Christ. Pelikan notes that a number of theologians not only explored the Incarnation as a requirement of redemption as Athanasius did in the early fourth century, but asserted that Incarnation was a metaphysical requirement, regardless of the particular religion. For them, the Incarnation was not merely a peculiar feature of the Christian religion, but a way to judge other religions wanting.