This [Gospel] is preached and submitted to the whole world, that they may learn to know this man [Jesus Christ] aright, and to know how to become Christians, not how to become good and innocent. Other doctrines outside of the Gospel, like the books of the heathen masters, insist that the people should through them become good; again, the legends of the saints especially insist that the people are to live as the saints lived. To make good people does not belong to the Gospel, for it only makes Christians. It takes much more to be a Christian than to be pious. A person can easily be pious, but not a Christian. A Christian knows nothing to say about his piety, for he finds in himself nothing good or pious. If he is to be pious, he must look for a different piety, a piety in some one else.
To this end Christ is presented to us as an inexhaustible fountain, who at all times overflows with pure goodness and grace. And for such goodness and kindness he accepts nothing, except that the good people, who acknowledge such kindness and grace, thank him for it, praise and love him, although others despise him for it. This is what he reaps from it. So one is not called a Christian because he does much, but because he receives something from Christ, draws from him and lets Christ only give to him. If one no longer receives anything from Christ, he is no longer a Christian, so that the name Christian continues to be based only on receiving, and not on giving and doing, and he receives nothing from any one except from Christ alone. If you look at what you do, you have already lost the Christian name. It is indeed true, that we are to do good works, help, advise and give to others; but no one is called a Christian by reason of that, nor is he on that account a Christian.
Martin Luther, Church Postil for Trinity 24 (Matthew 9:18-26)