I've just finished reading "The Swerve" by Stephen Greenblatt. It's a fascinating account of how in the early 15th century a copy of "On the Nature of Things" by the Roman author Lucretius was discovered in a remote monastery. The book is a powerful and passionate poem inspired by the Greek philosopher Epicurus and had long been thought to be lost forever.
Greenblatt brilliantly conjures up the atmosphere of late medieval Europe by writing about the life and times of the man, Poggio Bracciolini, who made the discovery. He goes on to describe how the prevailing theology of the day was challenged by exposure to the ideas of Epicurus and makes a good case that "On the Nature of Things" was one of the drivers towards the more enlightened ideas we have today. I encourage you to read "The Swerve" as Lucretius' original "De Rerum Natura" is possibly a little inaccessible unless you happen to be a Latin scholar.
For me the deepest impression was about the contrast between the philosophy of Epicurus and the teachings of the Christian churches.
We tend to think that "Epicurean" means unthinking abandonment to licentiousness. But that completely distorts the Epicurean message. Indeed that message does advocate that one should pursue pleasure. However, the point of the pursuit is to live life to the full because this life is all there is. So not only the bodily passions are important but also the passions of the mind and the satisfactions of creating and living out one's own thoughtful purposes. Everything is made of atoms and when our body dies the atoms are reformed. The soul is also made of atoms and it too does not survive our deaths. Isn't that incredibly modern?
Contrast that with the central message of Christianity: bear your privations in this life so that you may enjoy the eternal one that follows (because if you don't you'll be enduring an infinite torment afterwards). I literally shudder to think of how many lives have been blighted by this message. How much effort has gone into refining the Christian dogma and imposing it on its adherents. We could have begun the enlightenment 1700 years earlier if the Christian religion had not had the supreme good luck to be adopted as Ancient Rome's official religion.
But don't read my ranting: go out and buy Stephen Greenblatt's masterpiece.