“Evangelism” became a business buzzword during the internet boom of the late 1990s. In fact, as Apple’s second software evangelist, I helped popularize the term. The idea is simple: Derived from a Greek word that means, roughly, “to proclaim good news,” evangelism is explaining to the world how your product or service can improve people’s lives.

A version of this article appeared in the May 2015 issue (pp.108–111) of Harvard Business Review.