When Luther questioned the notion of God according to the Catholic Church, this was significant because it questions whether the Catholic Church was actually preaching the correct will of God.
The prevailing method by which the Catholic Church had spread God's word was through fear - the fear of hell. When Luther questioned this and instead said God was merciful, he essentially questioned the legitimacy of the Catholic Church because he preached what they didn't.
Find out more on Luther at https://brainly.com/question/904226.