Luther acknowledged that the idea of God willing humans to sin seemed clearly to suggest that He was, therefore, the cause of sin. To continue to insist that God had also made the law and expects humans to keep it creates intense conflict. Luther's response to such a dilemma? 'This is too deep for us. God's will is involved, but I am not supposed to know how this all happens.'
Yes, we all struggle with this, don't we? I'm glad the dead guys struggled with it, too!