We believe that God’s Word is God’s power to work in our lives. With the word of His Law (the Ten Commandments), God shows us our sin and our need for a Savior. With the word of His Gospel (the “good news” of Jesus and His work for us) God forgives us for Jesus’ sake. (Matthew 28:18-20, Romans 1:16-17, Romans 10:17)
Christ’s Spirit must not only comfort but also through the office of the Law “convict the world concerning sin” [John 16:8]. In the New Testament, as the prophet says, He must do the work of another (reprove), in order that He may afterward do His own work which is to comfort and to preach grace. To this end, the Spirit was obtained for us through Christ and sent. For this reason, He is also the Comforter, as Dr. Luther has explained in his comments on the Gospel for the Fifth Sunday after Trinity, in the following words: “Anything that preaches about our sins and God’s wrath (let it be done however or whenever it will), that is all the preaching of the Law. Again, the Gospel is such preaching as shows and gives nothing else than grace and forgiveness in Christ. Yet it is true and right that the apostles and preachers of the Gospel (as Christ Himself also did) confirm the preaching of the Law. They begin the Law with those who do not yet acknowledge their sins nor are terrified at God’s wrath; as Jesus says, ‘When [the Holy Spirit] comes, he will convict the world concerning sin … because they do not believe in Me’ (John 16:8-9). Yes, what more forceful, more terrible declaration and preaching of God’s wrath against sin is there than the suffering and death of Christ, His Son? But as long as all this preaches God’s wrath and terrifies people, it is not yet the preaching of the Gospel nor Christ’s own preaching, but that of Moses and the Law against the impenitent. For the Gospel and Christ were never ordained and given for the purpose of terrifying and condemning, but for comforting and cheering those who are terrified and timid.” (Formula of Concord: Article 5, Paragraphs 11-12)