Why and how did europeans openly challenge the catholic church, church doctrine, and the bible?

With the invention of the printing press the knowledge was made easier to spread which led to greater education and greater social mobility. This also made the Bible accessible to more people. People were looking for more personalized approach to their spiritual needs. It was Martin Luther who made openly challenged the teachings of the Catholic Church by posting his famous thesis against the selling of indulgences. After they branded him a heretic he denied the idea that the Church is a mediator between God and man. 

By the time of the Reformation, European society was experiencing greater social mobility. The rising middle class was challenging the established social order. Humanists stressed the central importance of individual talents and performance regardless of noble descent. Printing made books widely available and facilitated access to the Bible for literate lay people. People were increasingly looking for a personalized approach to religion to accommodate diverse spiritual needs and guide individuals in their quest for salvation.
   Martin Luther, a pious German Augustinian monk and a professor of theology who was of modest middle class origin, resented the indulgences, which he found incompatible with a personal connection to God. He posted his objections. Because he was a forceful and effective writer in both German and Latin, he soon became very popular with the German reading public. When the Papacy denounced him as a dangerous heretic, he responded by denying the notion of clergy as a separate estate and the Church's claims to be the sole mediator between people and God. He stressed the importance of the individual believer's conscience and faith. He also translated the Bible into German and argued that Scripture as the Word of God was much more reliable than Church traditions. His numerous followers formed their own religious communities, creating Protestantism as an independent religion.