That does look a very worthy book, although I imagine requiring considerable concentration as it seems to cover a lot of ground.
I feel as though at the basis of many of the vexed debates on this subject is the basic Christian belief in the ‘one truth faith’ — with the implication that to differ from it is to be condemned. That anyway is the basis of ‘exclusivism’ (that Christianity is the only path to truth). That informs even the vehemence of a lot of atheist polemic, as it is forced dichotomy in some sense. After all, many have suffered in times past for straying from the orthodox path, where orthodoxy means ‘right belief’ or ‘right worship’, created against the background of a very narrow path.
Here I will refer to an essay by James S. Cutsinger, Professor of Religious Studies (died 2020) a discipline which is nearer my own orientation than either philosophy or theology. He has an entry in this book called Perennial Philosophy and Christianity, which takes issue with the ‘exclusivist’ view which (some will say) typifies Christianity.
The philosophia perennis, he says, was a term coined in the early modern period and taken up by Liebniz:
Comparing this truth to a perennial flower, a perennialist asserts that there is one divine Source of all wisdom, which has repeatedly blossomed forth throughout history. The major religions, including Hinduism, Buddhism, Taoism, Judaism, Christianity, and Islam, are different forms of that wisdom and are sometimes referred to as paths leading to the same summit or dialects of a common language.
It was the subject of Alduous Huxley’s popular book of that name (published 1946) and greatly elaborated by a diverse group of 20th century scholars and historians generally known as the traditionalist school. But the point the essay makes, is how to square the universalism of the perennial philosophy with the ‘one true Faith’.
Cutsinger argues that the exclusivist reading of Christ — which ties salvation exclusively to the historical events of first-century Palestine — rests on a Christological error. The true subject of Christ’s words and actions, as established by the ecumenical councils, is the eternal Word or Son of God, the second Person of the Trinity, not a particular historical individual. This means the famous “I am the way” declaration of John 14:6 is spoken by the pre-existent, cosmic Son — the same Person who says “before Abraham was, I am” — and cannot be straightforwardly confined to a singular historical manifestation. Drawing especially on Cyril of Alexandria’s reading of Chalcedon, Cutsinger insists that the Jesus of history is the cosmic Christ: there is no separate historical person standing alongside the eternal Son. What the incarnation presents is not an individual man but human nature as such, assumed into and divinized by God. It follows that the saving work of this one Son need not be restricted to Christianity: the Word may be salvifically operative in other authentic traditions as well, appearing personally in figures such as the Hindu avatars and impersonally in the Qur’an — not as a demotion of Christ, but as a recognition that his power and scope are vastly greater than a narrowly exclusivist reading had allowed.
I daresay an interpretation that not many Christians, especially those leaning towards fundamentalism, would accept, but I think makes a better background for the kind of pluralistic understanding that today’s secular culture requires.