[Ali Imran]

Word of his teachings spread to Jewish communities across the empire. This was helped by energetic apostles, such as Paul 

Paul had followers but he wasn't successful as a movement because his teachings were opposed by the disciples and as I've said, the believers in Jesus would have naturally followed the disciples rather than Paul. But after a few decades, Paul's teachings which is more appealing for obvious reasons began to gather followers but still not enough to put out the opposition, the followers of the disciples. 

It was when Constantine took on Pauline's Christianity that they suddenly became strong and the opposition was hunted down and defeated. The opposition went underground but eventually, they lost out and disappeared. That's why we find their scriptures underground and hidden away. And that's how Pauline's Christianity became the official religion.

That's the gist of it.