From Steve Rundle and Tom Steffen’s Great Commission Companies:

Using business as a vehicle for missions and ministry is not new. The apostle Paul, for example, was a full-time leather worker during much of his missionary career. A study of his letters reveals that working was more than a way to support himself; it was a central part of his missionary strategy. Preaching the gospel for free added credibility to his message and served as a model for his converts to follow.