In Homers epic poems the Odyssey and the Iliad show that the ancient Greeks valued duty and honor above most other things. In the Odyssey and the Iliad the gods were portrayed as often changing their minds, being petty or vain. Some philosopher strongly disagreed with this however. The pre Socratic philosopher Xenophanes said that if there were gods (or god) that they would be higher than human beings and more noble. Socrates and Plato did not openly oppose the Greek religion but they developed a moral philosophy so appealing that it made people wonder why they should worship their vain and petty gods. By the Roman times people were looking for a religion that would appeal to the heart and to the mind. Stoic philosophy was popular among the intellectual but it did not hold much appeal for the common man because of the detached way you were supposed to look at life. They were also wondering about life after death and what that might look like if it was real.
This paved the way for Christianity to come in and to be spread rapidly. Some of the great ancient thinkers, such as Socrates and Plato had alluded to the fact that there might be a higher power unlike the gods of that day. The values of the Greeks had been rather self centered focusing on your own honor and prosperity. These differed from the values of Christianity that you should be humble and to place others before yourself. The Greeks had hoped to be good people to get into the Elysian fields of the underworld where there were none of the tortures that there were for the wicked people. This contrasts with the Christian promise that if you put your faith in Jesus as your savior, you will be saved.