When Christianity was introduced it faced an obstacle. There were already religions and gods everywhere. What we now call Paganism had been established for centuries.
Why did Christianity thrive during these early ten centuries of its life and is no longer growing. Today there are billions available for conversion just like there were millions back then.
I’ve been trying to understand what happened. There was the Roman Empire then and a Roman dictator who converted. This had to help, but growth of the faith may have happened anyway.