It’s important to recognize that philosophy is an evolution of theology. And like any evolutionary iteration, it required certain conditions to be fulfilled before it could really take hold. I’ll deal with the similarities first.
The same kind of thought goes into theology as in philosophy. The aspect that makes them similar is rigor. You can learn it in colleges and universities, and there is religious philosophy that greatly informs the more supernaturally-focused theology. You can use the rigorous nature of the material to analyze and come to a conclusion of theological ideas, the same way you might develop a scientific theory. You just don’t use scientific experimentation to do so, as science is empirical, focused on the senses, while theology focuses on the world of the mind.
The original Greeks who devised philos were extremely religious, participating in the rituals and rites of their day, they were simply curious if understanding could be obtained independently of the priests. The Stoics acknowledged traditional views on cosmogony.
Even Thales, hailed as the world’s first philosopher, is widely considered to have believed in the dominant Orphic cosmogony, and wanted to prove the assertions, as he had been visited Egypt and brought back observations he’d made of their mathematics. These efforts led to the methods, practices, and theories that we now call science, philosophy, and epistemology.
Philosophy and religion have coexisted, collaborated, and informed each other ever since philosophy’s development. Christianity owes a great debt to Hellenistic ideas, particularly Platonic idealism, which was immensely important to the eventual separation of the Christian Church from the Judaic establishment. Christian ethics initially played a great role in civilizing the European barbarian warlords, then got corrupted along with them as the Papacy succumbed to greed and vice. It took a refresh and infusion of new philosophical ideas to reform the Christian world.
All the questions and debates the Reformation started, fed into the growing movement towards defining society and the state on top of a secular, humanistic ideology, which can be rightly seen as a purification and synthesis of religious ideas that began in the Reformation.
So we’ve seen how they interact and inform each other due to their shared aims, describing and understanding fundamental existence, so how do they differ? Well, when the Greeks were devising philosophy, they started with the idea of wisdom, and ended with a conception of knowledge.
Before the Greeks, all people cared about was efficacy, and for good reason. There just wasn’t enough wealth around for people to just sit around and think about random things. And their societies just weren’t set up for that. The Egyptians had a sprawling theocracy with immensely rigid and numerous social classes that radiated out from Pharaoh, who was the gods chosen emissary to the people, who owned all the land, whose authority was absolute.
There just wasn’t any interest in separating out wisdom from theocratic origins. None of the ancient societies, all over the world, save the Greeks, managed to do this. All higher ideas were ascribed to the gods. Only when philosophically-inspired Christian ideas started spreading throughout the world as universities started cropping up in the 10th century did the rest of the world really start grappling with the difference.
So what’s the core difference between philosophy and religion? Well it’s simple and boring when you get down to it. Theology considers divine agency, where God can be an originator of events. While philosophy seeks to understand events and their causation outside of the frame that God is the ultimate mover and shaker.
And so when you think about it, you can see how intertwined the two were throughout history. Philosophically-derived modes of examination were limited to what could be observed and reasoned about. Theology could move faster, by simply ascribing a cause and effect magisterium that allowed people to just get on with it. When it came time to come up with ideas to organize society, to divide up resources and access to privilege and perks, religion shined. Philosophical modes would have to wait until the 1800s before it could really hit its humanistic stride.
As philosophy and humanism continued to examine the roles of elites throughout society, and common people found organization and purpose and political agency, they invariably clashed with the establishment, producing the modern age. Modernity saw excesses in all things run rampant over the Earth. Wars had been fought for hundreds of years in Europe according to Christian ethics. That all ended when the French citizenry, feeling besieged by the surrounding traditional monarchical states, fought a series of wars to assert themselves on the global stage as a republic. A government founded, not on the idea of a divinely-created king, but legitimized by a grassroots constituency.
Religion began fading from the public consciousness, but it never quite went away. Because at the end of the day, there’s a fundamental human yearning for more. This inevitably leads to the divine. Religion and philosophy should be seen as two interrelated ways of investigating anything and everything desired. Then you can see the recent phenomena of superheroes and science fiction and fantasy as evolutionary iterations on ancient myth. The monotheistic deity, along with beings that live between us and the deity, are not so easily dispelled from society. We’ll just invent more. And philosophy will intertwine with the theologies of the new gods to inform our culture and how we see ourselves in the grand scheme of things, just like they’ve done for millenia.