Some think of a personal testimony as evangelism. Certainly a testimony of what God has done in our lives may include the Good News, but it also may not include it. In telling other people how much Jesus means to you, you may not have told them the Gospel at all. Have you explained what Christ did by dying on the Cross? It is good to share your own testimony of what God has done in your life, but in your testimony, you may not actually make it clear what Christ’s claims are on other people.
Testimony is, of course, very popular in our postmodern, “that’s-good-for-you” age. Who would object to your thinking you’ve gotten something good from Christ? But wait and see what happens when you try to move the conversation from what Jesus has done for you to the facts of the life, death, and resurrection of Christ and how that all applies to your nonbelieving friend. That’s when you discover that testimony is not necessarily evangelism.
— Mark Dever, from Nine Marks of a Healthy Church, p. 133