Natural Theology

 When Tennyson sat his Cambridge entrance examination, it consisted of four subjects – Latin, Greek, Algebra and Natural Theology. Of those, the first two are in steep decline, especially Greek, though 'classical studies' in various forms are still on the curriculum. Certainly the days are long gone when an easy familiarity with Latin and Greek, with ancient history and classical mythology, were part of every educated man's (and many women's) mental world. Algebra, I presume, survives as a branch of mathematics (one I could never master), and was perhaps regarded as a useful training in abstract reasoning. As for natural theology, surely nobody now would regard it as a 'core subject', but rather as something that might turn up in theology or philosophy courses, or perhaps in the study of the history of science. However, for much of the 19th century, and into the 20th, natural theology was very much alive. It's a form of theology that seeks to demonstrate that theological ideas – especially of the existence of God – can be reached by way of reason alone; that there is no need for revelation. The most famous exemplar of this approach was William Paley, whose Natural Theology, or Evidences of the Existence and Attributes of the Deity collected from the Appearances of Nature was a hugely popular and influential book. But there was always strong criticism from the likes of Hume, Kant, Kierkegaard and, more recently, Karl Barth. Not to mention God Himself, who in Psalm 50 rebukes the wicked for thinking that He is just like one of them: 'Thou thoughtest that I was altogether such an one as thyself'. This quotation stands at the head of a knotty, punishingly long poem by Browning – 'Caliban Upon Setebos; or, Natural Theology in the Island'. In this, Shakespeare's Caliban attempts to understand the god he worships, Setebos, through observing how the natural world works, and inevitably finds himself looking in a mirror, discovering a cruel god of arbitrary and jealous power, lording it over nature just as he does himself in his smaller realm. Here's a link to the poem, if you're feeling strong...  
https://www.poetryfoundation.org/poems/43748/caliban-upon-setebos

Some trace of natural theology perhaps survives in the idea that there are inherent 'Laws of Nature' or 'natural rights'...