Marcus Tullius Cicero [106 BCE – 43 BCE]:
A human being was endowed by the supreme god with a grand status at the time of its creation. It alone of all types and varieties of animate creatures has a share in reason and thought, which all the others lack. What is there, not just in humans, but in all heaven and earth, more divine than reason? When it has matured and come to perfection, it is properly named wisdom. . . . Reason forms the bond between human and god.The Romans didn't use capital letters, so we can't know if Cicero would have capitalized "God." [What did he mean by the supreme god? If they used capital letters, would He get one?]
What we do know is that from Aristotle to Thomas Aquinas [natch!] to John Locke to Thomas Paine, man's reason is believed to be God-given---and when a man uses "right reason," he participates in the divine. God is logical, and doesn't violate his own rules, cannot violate logic. The universe makes sense. There is a [one] God and it all makes sense if you tap your noodle. Theistic rationalism. The best of the Greek and Roman traditions were Aristotle and Cicero, culminating here in what is called "natural theology." Not just Aquinas but the early Church---and Paul the Apostle of the epistles---saw Christianity as the fulfillment of not just the Hebrew scriptures, but of the best of Greco-Roman theo-philosophy---of reason itself!
Reason meets revelation, the philosophers shake hands with the scriptures. What's not to like?
There's nothing wrong with "theistic rationalism" as a descriptive term but it was "natural theology" long before the American Founding, and as we see, it fits Christians and non-Christians as well. It tells us something, but not enough. John Locke is more religious---Christian---than Aristotle.
That's all. No big revelation here. And you don't need the "divine revelation" of holy books like the Bible to figure out what "right reason" might be. Aristotle, Cicero and Paine all stipulated the idea that truth---and a natural law---exist without divine revelation [Paine despite it!], i.e., a Bible. The sky is blue. These days not so much, but back in the Founding days, they all agreed it was.
[Whatever "blue" means, but that's another discussion, eh?]