[P]roperly divided law and Gospel uses the Gospel alone to motivate. Earlier was cited the error of trying to motivate by the Law. While the Law can instruct as to what good works are, only the Gospel can motivate people to do them.
Law motivation is characterized by the imperative mood. Similarly, a sermon dominated by ‘shoulds’ and ‘musts’ and ‘let us’ seeks to motivate by the Law. The indicative mood is generally more appropriate to the Gospel. Declaring what Christ has done to redeem the sinner moves his heart to respond in sincere good works.
Special care is necessary to avoid turning narratives rich in Gospel into motivations of Law. Narratives recounting the actions of great Bible figures, including Christ, can easily be mispreached as mere examples for today’s people to follow. The stories become implied or expressed imperatives (‘Be like Daniel!’), rather than illustrations of how God enables his people to accomplish great things. Particularly in preaching the events of Jesus’ life, his vicarious acts for mankind are too easily reduced to examples to emulate. Properly divided Law and Gospel will emphasize God’s gracious work so that hearers will be motivated to Christ-like living by faith.”
Dr. Carl C. Fickenscher, “The Relationship of Sermon Form to the Communication of the Proper Distinction between Law and Gospel in Lutheran Preaching”