The would be three main factors here.
1. The Catholic practice of selling indulgences for money angered many, especially Martin Luther who would later start the wave of Protestantism across the Europe. The tipping point was selling indulgences for a donation to the renovation of the St. Peter Cathedral in Rome.
2. The economic position of the many at the time was very bad which was due to the fluctuating economy. This made people more open to the new ideas.
3. The creation and the advent of the printing press which we can say democratized knowledge as it made available many pamphlets and books to the much wider audience thus spreading knowledge.