Why Did Martin Luther Challenge The Church

Martin Luther challenge the church because he had wanted them to stop selling indulgences. This information was gathered from a famous letter that Martin wrote to the Archbishop talking about how it isn't right to be having the indulgences including the sentence, “ The unhappy souls believe that if they have purchased letters of Indulgence they are sure of their salvation.” Another reason as to why Martin challenge the church this way is how its tone is written in the letter as opposed to the other informational document. The letter, was written in a respect and determined toned calling the Archbishop a distinguished and sublimity person. Unlike in the other informational document, which is a private conversation written 30 years after.
I trust the first informational document because it's was known to everyone unlike the other. Also the other one isn't in a respectful tone like the letter. To recollect, Martin Luther challenge the church because he had wanted them to stop selling indulgences.