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.
Therefore, if you wish to consider the word in its true meaning, you must identify a Christian by the fact that he only receives something from Christ, and has Christ within him; for this is what the word properly means. Just as a person is called “white,” because of his white color, black because of his dark color, large because of his size. So also one is called a “Christian” because of Christ, who dwells in him and from whom he receives his blessings. So, if one is called a Christian because of Christ, he is certainly then not called a Christian because of his works. From this it also follows that no one is called a Christian by reason of his good works. If this be true, as it undoubtedly is, then it must follow that our orders and sects do not belong under the Christian name, and they do not develop Christians.
Therefore they are deceivers, who preach or teach in the church, and occupy themselves with commandments, works and statutes, that accomplish nothing. Although they pretend to be Christians, nevertheless they still, under this name, attempt to burden and torment us with their commands and works. By reason of my works I may well be called one who fasts, one who prays, or a pilgrim, but not a Christian. If you were to weave all your works together, and add to them all the works of others, you would still not have Christ, and from these things you could not be called a Christian. Christ is something different and higher than law and the commandments of men. He is the Son of God, who is ready alone to give and not to receive. If I am so wise as to take what he offers, I have him, and if I have him I am then justly called a Christian. Thus you have the distinction as to what a Christian is and what Christ is.
Martin Luther, First Church Postil for Trinity 24 (Matthew 9:18-26)