I Thessalonians 4:12
That ye may walk honestly toward them that are without, and that ye may have lack of nothing.
This idea includes honest financial transactions, but a good deal more. People outside of Christ have a right to watch the conduct of professing Christians in business life, domestic life, social life, political life, etc., and expect to see the evidence of the presence, person, and power of Jesus Christ at work. Then, in living for Christ, we have the promise of His provision as well.