The church had lots of power during this time. Probably too much. There were dishonest things going on around the church, more and more so as the availability of printed material increased. The church even began selling indulgences (paying money to get out of trouble with god).
I think that humanism and the printing press directly spurred the protestant reformation. More people could read- and therefore think for themselves instead of being told. Because of the printing press, the reading was available, and less costly. People began criticizing the bible, and reading it in different terms than before.
Martin Luther started the reformation. There were false documents being made, and many un-churchly things going on at church. Martin Luther wanted to stop the corruption. He also wanted to be able to interpret the bible himself, and allow the people to interpret it their own way, and so he had the first german language printed bibles.