Among the hundreds (if not thousands) of competing religious beliefs, practices, rituals, and faiths in the developing years of early Christianity--and arguably against all odds--Christian monotheism won. For awhile, the thoroughly pagan Roman Empire became officially Christianized.
Could it be a simple fact?
1. Jews did not evangelize, kept to themselves, and treated outsiders as unclean. How was Judaism going to grow by any other means but pregnant Jewish women having lots of children?
2. Pagans had no problem at all accepting any and all beliefs simultaneously because polytheism was 'normal' and conventional. Christians were seen as 'atheists' due to the fact they DID NOT BELIEVE in ALL the gods (except their own.)
3. In a worldwide marketplace of ideas, EVANGELISTS who bad-mouthed competing religions had a remarkable advantage.
A missionary religion that insisted it was right and all others were wrong won out because: as it spread, and gained converts, it destroyed all the other religions in its wake. Unlike other religions that spread throughout the Roman world, as Christianity grew, it necessarily shrunk all its competitors.
How did Christianity shrink all its competitors?
Suppose I am a Christian evangelist trying to convince a crowd of a hundred pagans that the God of Jesus alone should be worshiped, and suppose I am competing with a pagan evangelist who is trying to convince, at the same time, the same hundred pagan people to start worshipping the God Apollo. And suppose each of us is equally successful so that I convince half the crowd to worship the God of Jesus and he convinces half to worship Apollo. In so doing, Christianity has gained fifty members and lost none, and paganism has lost fifty members and gained none! (This example is suggested by the book, Ramsey MacMullen’s Christianizing the Roman Empire.)
As Christianity grows, the other religions shrink because Christianity is exclusive in its claims. Over time, that starts mattering. And as converts begin to increase, Christianity starts not only to grow but to overwhelm the opposition.
SCARY THOUGHT OF THE DAY: Jehovah's Witnesses' extreme evangelizing and exclusions border on the pathological. Could this strategy be the sole reason such cults as JW's, Mormons, and the phobic Islam, are growing like weeds in an untended garden?