For some time I was under the impression that the prospect of eternal punishment for the wicked and eternal paradise for the righteous was the "selling point". But there was Tartarus and Elysium and, by the time of Virgil, the Underworld was compartmentalized in a way that was almost Dantean.

By the time of the Diocletianic Persecution, there were Roman senators that had abandoned Jupiter Capitolinus for the church. What caused them to inherit the god and religious texts of the cult of an alien, foreign people, with a main character who was killed by the lowest form of capital punishment the Romans had, and a god that was mutually exclusive not just to the worship of other gods but to the recognition of their very existence?