Once I met someone promoting a certain product, telling how wonderful and useful it was. I asked him if he owned and used one himself. He admitted that he did not, but knew about the product well. Right there and then, he lost much of his credibility. This makes me realize that if we only tell others how great God is, but not mention how he has changed our lives in any way, we can't be very convincing. Giving personal testimonies is an effective way of backing up what you preach. To spread what God has done to and for you is to glorify God, something to boast about. Catholics can learn much from their Protestant brothers and sisters.