“Whether our contrition is genuine or not is a question which cannot be left to our own discretion, but must be left to the judgment of God. Therefore, no one can say without presumption that he is truly contrite.
“…If a man were required to say that he was truly contrite, he would be driven to presumption and to the impossible task of knowing all sin and evil in his heart. And since all the saints still have sin and evil within them, it is impossible for anyone to have such contrition as will be adequate in God’s judgment… …If no one will be found justified, how will anyone be found contrite, since contrition is the beginning of justification?
“… God’s promise in the sacrament is sure; our contrition is never sure. For this reason God would have us build not on our uncertain contrition, but on his certain promise, so that we may be able to persevere in every time of trouble” (“Defense and Explanation of All the Articles”, LW 32, 55).