Martin Luther's quote "Reason is the opponent of faith" suggests that faith and reason are incompatible. He thought that faith is based on trust and belief in something that can not be proven, while reason is based upon facts and proof. Reasoning can cause question and questioning, which can undermine faith. Luther believed that faith ought to be based on trust in God, not on sensible reasoning. He argued that faith must be accepted without question, and that reason needs to not be utilized to challenge it. He believed that faith should be accepted on faith alone, and that factor must not be used to try to comprehend it. Luther's quote is a tip that faith should be based on trust and belief, not on sensible reasoning.
