The sacrifices of God are a broken spirit;
a broken and contrite heart, O God, you will not despise. (Psalm 51:17)
This statement must also be dealt with negatively. Because it is a pleasing sacrifice to God if in our sadness and contrition we hope for mercy, therefore He forbids despair as the highest wickedness. He wants us to bear the tribulation in faith; He does not want us to add despair. Presumption about our own righteousness and despair about our own unworthiness are equally great sins. We must hold to the middle way, otherwise the most pleasing sacrifice can become the highest abomination. The sacrifice should remain a sacrifice and not become a destruction when we despair. Each of us should bear his cross and affliction so that we are not crushed by our sorrows and fall into despair; for that would rob God of His divinity, which He shows primarily in His mercy, as the definition of this verse proves. Every day we say and teach this, but when it comes to practice, very few perform it, but like cowardly soldiers we desert the colors at almost the first feeling of temptation. We should stand in our trust in mercy when we seem to be crushed by sorrows, and complete the sacrifice which the Holy Spirit so commends to us. Here there is a place even for the weak, just so they do not completely forsake their station. Nor is anyone master of this art, but we all remain disciples, as Paul also says (Phil. 3:12): “Not that I have already obtained or am already perfect, but I press on.”
Martin Luther, Luther’s Works v. 12 406-407