The main idea was that believers could only be saved by their faith, not their deeds, and that they should repent to God instead of a priest. This idea was major because it meant that you could find salvation independent from the church and emphasized a more personal relationship with God.
Explanation:
In his thesis, Luther protested a lot of what the church was doing including confessions and indulgences. In his time, it was common for people to pay the priests to "forgive" or put in a good word about them when they talked to God or even reserve a place for them in Heaven. Having studied his Bible, Luther found that these practices weren't biblical and godly and made this known to the people who were being scammed.
Popular legend has it that on October 31, 1517 Luther defiantly nailed a copy of his 95 Theses to the door of the Wittenberg Castle church. The 95 Theses, which would later become the foundation of the Protestant Reformation, were written in a remarkably humble and academic tone, questioning rather than accusing.
