1) Luther had a case of scruples for a lot of his life. He had a hard time feeling forgiveness for his sins and feeling God's love. Maybe his reason for putting so much emphasis on faith?
2) Luther believed that having faith will lead to good works - they naturally belong together and cannot be separated!
3) Luther wrote a lot about the law, and what it means for us after the resurrection of Jesus and the beginning of a time of freedom from sin. He said that the difference between following the law and fulfilling the law is faith. Maybe this was why he often wrote of faith alone - faith alone is what transcends the gap between following and fulfilling.
Well, that's honestly all I have to share! For a guy whose theology led to many churches who don't emphasize a life change and only tell the parishioners to have faith, I found it interesting that this is not even close to what he meant. Just something to think about as you wrestle with justification :)
Finally, a little Michael Bublé for you! Love this song and love him, awww yeah.