One of the Challenges that Christ presents to us is this: You ought to be a witness if you are in Christ. It does not mean you can never sin. But it rather means that because of the new nature, Christ's Nature, that lives within you, you can't continue to stay in sin or feel happy when you sin. You have within you the urge to be Christlike all the time. In keeping with that consciousness, you will always want to be a witness for Christ.In Matthew 5:13-16. Jesus teaches that his followers are to be a light unto the world.