Some quotes from the essay “Law and Gospel” in Letters to Lutheran Pastors: Volume 3”
For the modern Christian, as for the world outside of the church, preaching God’s Word and administering the Sacraments of Baptism and the Lord’s Supper are distasteful to the point of being offensive. The modern Christian knows no more what the church’s real responsibilities are than what they really mean. The world makes fun of the church because its only task is preaching. To this we answer that the world does not know the power of the divine Word. It does not recognize that behind the feeble words of human beings is the almighty Word of the Almighty God, which “is like a fire,” the “living and active” Word, which “is sharper than any two– edged sword,” which “pierces through to the division of the soul and spirit, of joints and marrow, and is the judge of thoughts and intentions of the heart” (Heb. 4: 12). How could the world have known, how can it know, that God created and still maintains the world through this Word? Quite literally all mankind lives because of this Word!
In the face of all the misunderstandings on the part of the world and all the errors which have arisen within Christendom, let us make this point absolutely clear: the task of the church in the world consists uniquely and alone in the preaching of the Word of God and in administering the Sacrament. All other functions which the church as a living organism develops and uses serve only to fulfill this task. All activities which the church can legitimately exercise in the world are by– products of preaching and the Sacraments. Christ had no other purpose in sending His church into the world than preaching and distributing the Sacraments. Only in accomplishing this task is the church recognizable as the church. In addressing this issue of identifying the basic church functions, the Reformation claimed that the marks of the church were the Word and the Sacraments. In these signs the church could be recognized. To be sure brotherly love, providing for the poor and the sick, moral discipline, prayer and worship will be present wherever the church is, but a fellowship (congregation) with only these marks is clearly unrecognizable as the church. Brotherly love can be found in the synagogue. The poor and the sick are provided for by modern secular governments. Moral discipline is a part of Buddhist monasteries. Prayer and worship are features of all religions in the world. The Gospel, Baptism, and the Lord’s Supper can be found only in the church. They are the indelible marks of the church (notae ecclesiae).
The moral sensitivities of the natural man are in no way satisfied by the Bible. It contains no system of ethics. No ethical ideal is held up as a standard. All the Bible’s moral injunctions can be found in other religions and philosophies [Weltanschauungen]. In fact, the moral sensitivity of the natural man finds the Bible offensive, because its central theme is that God accepts sinners and only sinners as righteous.
For if Christendom itself is so under the influence of modern culture and its anthropology so lacking in understanding that it no longer comprehends the depth of human sin, then it is high time that it earnestly puts this question to the church of the past, especially the church of the Reformation: “Have you ever considered, have you ever pondered, the enormity of sin?”
Only the person who has fearfully and earnestly taken up the question of sin and forgiveness can really understand what the church’s message is all about. Whoever has not come to this point– and this is especially true of the modern man since the Enlightenment with very few exceptions– must think the church’s message insane or must twist it around to make some kind of sense out of it.
God is not gracious to us because we have improved our lives or because we have made moral progress. In fact, we keep only a small part of His Commandments. He is gracious only and solely because Christ died for us and because His righteousness has become our righteousness. On the Last Day, salvation will not be given to those who have fulfilled the Law, but to those who fed and gave drink and sheltered Christ in the least of their brothers (Matthew 25). They have no knowledge of what they have done (vv. 38– 39). Everywhere in the preaching of Jesus it is clear that “the reward in heaven” is a completely unearned reward. At this point the Law and the Gospel come to a parting of the ways. This distinction does not mean that one has nothing to do with the other. They are both God’s Word. Both belong to the Old as well as to the New Testament. The Gospel as the promise of the coming Redeemer is already present in the Old Testament. Similarly, the Law does not cease to exist in the New Testament, though Christ is the end of the Law, that is, He is the end of the Law as a way of salvation. To be sure, Jesus preached the Law alongside of the Gospel, for example, in the Sermon on the Mount, in the announcements of divine wrath and the Day of Judgment. So the Law and the Gospel together both belong to the Word of God. Without the preaching of the Law there is no preaching of the Gospel. There is no authentic preaching of the Law in the sermon unless there is something of the Gospel there. For example, Luther sees Gospel in the introduction to the First Commandment. He understands the words “I am the Lord Your God” as Gospel. On that account the reformer can correctly say: “Within Christendom two sermons must be preached: the first is the teaching of the Law or the Ten Commandments and the other is about the grace of Christ (Gospel). Because where either Law or Gospel is incorrectly preached, the other is ruined. Where one goes down, the other goes under with it. On the other hand, where one remains in place and is properly set forth, it brings the other along with it.”
Since the eighteenth century Enlightenment, modern man has seen Jesus Christ only as a religious teacher with a moral agenda. The essence of the Gospel as the teaching of Jesus is its proclamation that the quintessence of religious truths is the truth that God is our Father and that we human beings are one another’s brothers. Similarly, the quintessence of ethical commandments is the double command of loving God and the neighbor and what is known as the Golden Rule (Matt. 7:12). Whether or not it was done deliberately, the uniqueness of the Gospel was taken out of it. Even the synagogue confesses God as our Father. Stoicism teaches that we men are brothers. The double command to love God and our neighbor is taken directly from the Old Testament, and the Golden Rule is a rational truth which every pagan recognizes or can recognize on his own. But in no way can these abstract religious truths produce the doctrine of the incarnation.
Between the Scylla of legalism and the Charybdis of antinomianism defines a narrow and dangerous path which the church must follow in her ethical thought. Whether she finds the way depends on the purity of her proclamation, and on this depends her existence. It is my wish that the World Conference of Churches meeting at Oxford  would be so endowed that churches of Christendom would serve in some way as a lighthouse on this way. Each of the churches must find its own way. They can only find their ways by turning away from the world’s tempting siren calls and in this benighted century to listen to the voice of Him who speaks to Christendom the same message which He spoke to the apostles and the reformers and which they believed: “I am the way” [John 14: 6].