He challenged the authority of the pope to offer the sale of indulgences directly. This was seen as an attack on the Church. Luther was summoned to Rome. He would have to answer to the charges of heresy he was accused of. Luther did not respond to the summons. That only led to an escalating controversy between Luther and those who defended the faithful document. Luther continued writing about salvation. He wrote about reforms that he saw needed to occur in the church. As a result of that, the rift between Luther and those who believed in him, fueled a growing controversy. (The 95 Theses of Martin Luther)
"The 95 Theses of Martin Luther (1517)." The Ninty-Five Theses of Martin Luther (1517). N.p., n.d. Web (http://www.crivoice.org/creed95theses.html)
Köstlin, Julius. The Life Of Martin Luther. 1st ed. 1883.