Martin Luther lived at a time when the Roman Catholic Church was extremely corrupt. Doesn't that look a bit like the way the Church is today? Anyway Luther thought there should be something better than Roman Catholicism of his time. First Luther tried to reform the Roman Catholic Church but when that didn't work he started Protestantism.
|“||"as soon as the coin in the coffer rings, the soul from purgatory springs."||”|
The Church persuaded people if they gave money to the their personal sins or the sins of other people they wanted to help would be forgiven. Luther thought the Church was too wealthy and made itself even wealthier by selling indulgences. The Church didn't like all this criticism and decided Luther was a Heretic. 
The Church or the Bible
Roman Catholicism taught and teaches that the Pope and other organs of the Church hierarchy are authoritative in interpreting the Bible, also establishing matters of Faith and doctrine. Naturally different Protestants interpreted the Bible differently and by the end of his life Luther disagreed strongly with some other influential Protestants. Disagreement between different Sects and denominations of Protestants have continued ever since.