The upright, in whom the law has exercised its work, when they feel their sickness and weakness, say: God will help me; I trust in him; I build upon him; he is my rock and hope.
There are two types of people who fulfill the law, or who imagine they fulfill it. The first are those who, when they have heard it, begin with outward works; they desire to perform and fulfill it by works. How do they proceed? They say: God has commanded you shall have one God; I surely will worship no other God; I will serve him and no idol and will have no heathen idolatrous image in my house or in my church. Such persons make a show with their glittering, fabricated service of God, like the clergy in our day, and they think they keep this law when they bend their knees and are able to sing and pray much. By this show the poor laity also are deceived; they follow after and also desire to obey the law by their works. But the blind guides the blind and both fall into a pit (Luke 6:39). This is the first type, who take hold and imagine they will keep the law, and yet they do not.
The other type is those who know themselves by the law and study what it seeks and requires. For instance, when the law speaks: “You shall have one God, and worship and honor him alone," this same heart meditates: What does this mean? Or what is it to have one God? It surely is something else than a bodily, outward reverence; and finally it perceives that is a very different thing than is generally supposed. It is nothing but having trust and hope in God, that he will help and assist in all anxiety and distress, in every temptation and adversity, that he will save him from sin, from death, from hell, and from the devil, without whose help and salvation he alone can do nothing. This is the meaning of having one God. A heart so thoroughly humble desires to have God. A heart that has become quite terrified and shaken by this commandment in its anxiety and trouble flees to God alone.
Now the hypocrites and work-saints, who lead a fine life before the world, are not able to do; for their confidence is based alone upon their own righteousness and outward piety. Therefore, when God attacks them with the law and causes the poor people to see that they have not kept the law, not the least of it, and when overwhelmed by anxiety and distress, and an evil conscience and they perceive that external works will not suffice and that keeping the commandments of God is a very different thing from what they thought; then they rush ahead and seek ever more and more works, and fancy that they will thereby quiet their conscience; but they greatly miss the right way. Hence it comes to pass that one wishes to do it by rosaries, another by fasting; this one by prayer and that one by torturing his body; one runs to St. James, another to Rome. They seek their end in so many ways that they can scarcely be enumerated.
Why do they do all this? Because they wish to save themselves, to rescue and help themselves. The consequence of this is great blasphemy of God, for they also boast mightily of these works, and vaunt and say: I have been in order so long, I have done this and that; God will give me heaven as a reward. Therefore you will find that there is nothing good in any man of himself. But you have this distinction, that the upright, in whom the law has exercised its work, when they feel their sickness and weakness, say: God will help me; I trust in him; I build upon him; he is my rock and hope. But the others, as hypocrites and work-saints, when trial, distress, and anxiety are at hand, lament and say: Oh, whither shall I go? They must at last despair of God, of themselves and their works, even if they have ever so many of them.
This is an excerpt from a collection of public domain sermons given by Martin Luther.