Why did the ancient Greeks and Romans stop believing in their gods? is a question on Quora.com. (This link will take you directly to this question on Quora.) Two helpful answers to be found there (and there may be others) are from Panagiotis Limnios and Tim O’Neill. They are giving the earthly perspective on that time period.
For those of you not signed up for Quora, here are excerpts – first from Tim’s answer:
Most ancient religion was more about communal practice than private, personal belief. People practised the religion of their community, their region and their political state and did so to ensure the gods they honoured protected them and sustained their communities.
Which gods you worshipped was, therefore, as much a function of where you lived, who your community (city, village, social class) worshipped and what religion was favoured by the state.You didn’t believe that other gods didn’t exist or that their cults were wrong, they were simply not as relevant to you.
Christianity changed all this by bringing in a far more exclusivist idea of religion from its parent religion, Judaism. To the Christians, the other gods weren’t just irrelevant, they were non-existent. Other cults weren’t just not useful, they were evil. This was one of the things which brought Christianity into conflict with the Roman state, which saw them as an insult to the protective gods of the Empire and therefore a threat to the state.
And here’s an excerpt from Panagiotis’ answer:
I’m surprised no one mentioned scripture, or, to be more precise, the lack of it.
Unlike Christianity, older religions had no authoritative text for people to draw inspiration or guidance from. Religious practice was dictated by custom, lacked completely a dogma and was so intertwined with ordinary social activities that it was indistinguishable from daily life.
The closest thing the ancient Greeks and Romans had to a Bible was Hesiod’s Theogony, and even that was by no means a comprehensive work since it dealt mostly with the story of their origin. There were so many gods, minor gods, deities and heroes, 30,000 according to Hesiod, that nobody even bothered to list them. People were simply content with praying to the few common gods of their family and community without worrying about making sense of it all.
Christianity not only polarized people by bringing “a far more exclusivist idea of religion” from Judaism (quote from Tim O’Neill), but it was also built from the ground up on scripture…
Of course, the spiritual backdrop of this era is the creation of new heavens and new earth prophesied in the Bible (Isaiah 65:17; 66:22; 2 Peter 3:13; Revelation 21:1) in which the heavenly powers which had fostered polytheism were deposed. Since then, monotheism has prevailed. For more biblical explanation of this, see Whatever Became of Jesus Christ?
Truly, as King Nebuchadnezzar learned, heaven rules in the affairs of men (Daniel 4:26).