What do you think made christianity attractive to the greco-roman world?
It was not attractive to the majority of the population until the worship of the Greek and Roman Gods was made illegal and the GOVERNMENT started actively supporting the Christian church in the destruction of the temples as well as the murder of those who followed the Olympian Gods. As a point of fact, it is STILL difficult, even with legally mandated freedom of religion in Greece, for followers of the Olympians to gain legal recognition. The lie of “No one worships the Ancient Gods anymore” is still the party line there, despite international organizations of Hellenic Polytheists who ARE still actively worshipping the Greek Gods.
It was spread through the slaves and women. It offered something attractive – a wonderful afterlife. That appealed because their lives on earth weren’t that great. Then it spread to the nobility through the wives. Then it became a tool for the powerful to lord over others and an excuse to conquer Europe and try to conquer the rest of the world.