When we are afflicted, and our conscience suffers conflict, the devil makes us afraid by the law and accuses us with the guilt of sin, our wicked past life, God’s wrath and judgment, hell, and eternal death. Thus he drives us to desperation, makes us bond-slaves to himself, and plucks us from Christ. Furthermore, he brings against us those passages of the Gospel in which Christ himself requires works of us and clearly threatens those who do not with damnation. If we are unable to judge between these two kinds of righteousness—if we do not by faith take hold of Christ as he sits at God’s right hand, interceding with the Father for us wretched sinners, then we are under the law and not under grace, and Christ is no more a Saviour, but a lawgiver. Then there will be no more salvation for us, but a certain desperation and everlasting death, unless repentance follows.
Martin Luther, Preface to Galatians