The theological interpretation of the law, as it applies to the internal condition of the sinner, is more severe than the civil use. Man can make restitution for violating the civil law, but he cannot do this in regard to the law’s condemnation of him as a sinner accountable to God. Luther’s explanations of the Ten Commandments are theological masterpieces which locate that moment when the law is fulfilled in Christ and then proceed to involve Christians as the are in Christ. Removing Christ from the equation of the sanctified life and the law results in people who are either morally self-satisfied or terrified by the law’s demands. Christians are not immune to moral self-satisfaction, but in the moment they come face to face with the accusations of the law self-confidence evaporates into dissatisfaction. So the Christian repents and in Christ he again fulfills the law in its positive dimensions. This is an endless cycle relieved only by death. In one moment the Christian is addressed as a sinner who cannot escape the negative prohibitions of the law, but at the same time the commandment addresses him as a saint who is taken back to the situation which existed in Paradise, in which he loves God and his neighbor. Since he is in Christ and Christ is in him, even before he becomes aware of the possibility of fulfilling the law, the Christian is actually doing so.
Luther’s interpretations of the Ten Commandments return them to their pristine sense as positive commands as they were known before the fall into sin. Law broken is not law fulfilled in Christ. All positive descriptions of the law in the Christian’s life are christological statements, things which Jesus did and which reached their perfection in Him. No Christian can achieve this in himself but only as he is in Christ. Fulfilled law is Christology as it describes the life and death of Jesus. He loved God with His whole heart, He prayed to God, He heard the Word of God and kept it, He honored His parents, He helped those in bodily distress, He loved the church as His bride, He lived a life of pure thoughts, He provided for those in distress, He spoke well of others, He had no evil desires. Jesus’ own description of Himself can in a certain sense be a description of the Christian’s life, the life lived under the third use of the law: “the blind receive their sight and the lame walk, lepers are cleansed and the deaf hear” (Matthew 11:5). Christian works of charity to the disabled are continuations of Christ’s works of mercy and certainly fulfill what Luther intends by saying that we should help our neighbors in their physical distress. Christ is the fulfillment of the law not only in the sense that all the Old Testament prophets spoke of Him, but He is the affirmation of what God requires of us and of what God is in Himself. In Christ the tension of the law and the gospel is resolved, and resolved also is the problem of how the law (third use) can be God’s last word to man.
Luther’s understanding of the commandments as christological affirmations recalls the parable of the Good Samaritan. He fulfilled the commandments not simply by refraining from a prohibited evil but by helping the the stricken traveler. Claims to moral perfection have little to do with understanding of the law, but the willingness to help those in distress, those who cannot provide help for themselves, belongs to the essence of the law in its purest form and to Christology. Law and gospel are distinct in diagnosing man as sinner and saint, but by being fulfilled in the gospel the law comes to the believer as a description of what he already is in Christ and as the promise of a perfect sanctification at death. Christ’s righteousness becomes his, and he performs good works with a cheerful spirit (third use). Thus one could say that the Christian wants to fulfill the law which is already part of his being by faith.
“Confessional Lutheran Dogmatics: Law and Gospel and The Means of Grace”, pages 68-69