[It was Christianity which taught that the universe is rational and comprehensible and that God does not act arbitrarily.]
Doesn't that go back to the ancient Greeks?
Curiously enough, philosophy was pretty much invented by the Greeks. The word comes from philo + sophia, and means the "love of wisdom." The traditional term for what we call science is natural philosophy.
But if you follow the history of philosophy, you will find that soon enough any significant development died among the Greeks, but was inherited by Christians. There was a Christian synthesis of what you might call Jerusalem, Athens, and Rome.
An article I read somewhere points out that serious philosophy has only been done over a sustained period of time in Christian universities. If you look a philosophy departments in our secular universities today, what you find is mostly dry, arid, and of interest only to other specialists.
Not many modern scientists are philosophers, but they rely on certain cultural assumptions that have been provided to them by philosophy, mostly conveyed through the Christian philosophical tradition.
Alfred North Whitehead doesn't get into all this background, but he does find a distinct debt of science to Christianity in the early modern period, when science and technology really took off.
Postmodernists, for instance, assume that the world is meaningless and that there is no purpose in life. That is not a helpful basis for rational thought.