Why did the church in Jerusalem prosper in the early years?
The church in Jerusalem prospered because the Eleven, later the Twelve, remained there, continuing the ministry Christ began. They stayed year in and year out, working among the Jews in Israel, giving that church stable, long-term leadership that Paul's brief church plants did not have.
Les explains that the Church of Jerusalem could prosper to a certain degree because the Eleven, and later the Twelve again, came back and continued the ministry that Christ began, and they stayed there year in and year out, working amongst those Jews in Israel. By contrast, Paul was not in any one place that long; every place he established a church, it was only for a week or two, and Antioch for a year and a half, before he moved on. Les points out that except for the miraculous working power of God, Christianity would have never gotten off the ground, especially among people so steeped in idolatry or Judaism. Jerusalem's stability came from the ongoing presence of the Eleven and Twelve.