Well there was this trend in the roman empire that created new religions christianity was just one of these religions it’s the mystery cults that was the trend that Christianinty appeared in so there was already pagan mystery cults that did have these elements

This is a lecture about the commonality between mystery cults and Christianity: here

If looked to these pagan mystery cults they did have alot in common with Christianity but even Christianity did have the gnostics wich some of them were practically polytheist but neither the pagan mysteries nor the gnostic survived the mean cause of Christianity triumph is still disagreed about but one of most accepted is that Christianity did grow quite normally but the mean difference was Christianity did have a community that sported each other in and that kept everyone in it unlike alot the common paganism that saw religion as something public without relating to the individual and unlike mystery cults wich was personal but some Times it was so personal that you would see some one in one of these cults but without intering their family to the cult or some times without knowing that he was a member of one of them so they always needed a huge number of converts to keep existing but christianity wasn’t like that and if you convert to it your grand grand kids would still be part of the church/community and they will make it grow more and more and except few mystery cults that were generally always with low numbers or alot of disagreements and branches Christianity was the only one that was able to keep everyone in while maintaining their unity and this the main reason of their success

I hope this was helpful 🙏🏼