Here are two events that significantly contributed to the rapid growth of Christianity:
* The conversion of Emperor Constantine: Constantine's Edict of Milan in 313 CE granted religious tolerance in the Roman Empire, effectively ending the persecution of Christians. His later favoring of Christianity provided it with political and social advantages, making it more appealing and accessible to people.
* Paul's missionary journeys: Paul of Tarsus was instrumental in spreading Christianity beyond its Jewish origins. His extensive travels throughout the Roman Empire, his establishment of churches in various communities, and his letters (which became part of the New Testament) were crucial in reaching a wider audience, particularly among Gentiles (non-Jews).