We should note that witnesses are, first of all, those who know something. They don’t just believe something.… If you have knowledge on any matter of great importance to human beings, it is your duty to make that knowledge available to others. If you know the house is on fire, you must share your knowledge with others. If you know where the bargains are, you tell your friends. If you know how to stop global warming or cure cancer you have a duty to share that knowledge. Not so of your mere opinions, feelings, or decisions about such matters.
—Dallas Willard, Knowing Christ Today