Martin Luther was initially a monk and priest who believed he needed to earn his salvation by being obedient to God and doing good works. He lived his life as if he would be judged worthy to enter heaven by the value of his earthly performance and behavior.
When Luther became a university professor, he had greater access to the Bible (they were not so common in those days). As he considered the words of Romans 1:17, "The righteous shall live by faith," he came to understand that you don't earn your righteousness by doing good works. You rather receive your righteousness from God through faith (in Jesus Christ). Thus, it wasn't a righteousness you earned, but one you received. The sinner receives the reputation of Christ's righteousness through faith and is then seen by God as possessing that righteousness himself.
As such, Luther believed you were not saved by faith and good works. Luther believed you were saved by faith alone! This became the cardinal teaching of Luther which paved the way for the Reformation and the establishment of all other Protestant denominations...and non-denominations!
Luther would retain the liturgical and traditional format of the worship service, but he would go on to purge the church of all doctrines and teachings which violated the Scriptures.