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.
"When the principles that run against your deepest convictions begin to win the day, then the battle is your calling, and peace has become sin. You must at the price of dearest peace lay your convictions bare before friend and enemy with all the fire of your faith"