Martin Luther and Assurance

"But you say, how can I be absolutely sure that all my works are pleasing to God, when at times I fall, talk,eat, drink and sleep too much, or otherwise transgress in ways I cannot avoid? Answer: This questions shows that you still regard faith as a work among other works and do not set it above all works. It is the highest work because it blots out these everyday sins and still stands fast by never doubting that God is so favorably disposed toward you that he overlooks such everyday failures and offenses. Yes, even if a deadly sin should arise (which, however, never or rarely happens to those who live in faith and trust in God), nonetheless faith always rises again and does not doubt that its sin is already gone. As it is written in 1 John 2 [:1-2], 'My dear children, I am writing this to you so that you may not sin; but if any one does sin, we have an advocate before God, Jesus Christ, who is the forgiveness for our sins.'" - Martin Luther, Treatise on Good Works