Why did christianity grow in the roman empire?

There are many reasons of why christianity grew in the Roman Empire. I'd go with these reasons:

1. Christianity were widely spread among poor people and slaves. Roman Empire was expanded and it was depended on slaves and poor.

2. Deceases spread all over the empire taking a lot of lifes, and people were inspired by the fact that there could be a life after death.

Christianity grow by people going to church and saying amen