C. S. Lewis wrote that
Faith is holding on to things your reason has once accepted, in spite of your changing moods.
When someone says “I can’t believe it’s Tuesday” he really means that he does believe it’s Tuesday, but it takes effort. His emotions are telling him that it is some other day, but he chooses to accept that it is Tuesday for other reasons.
It takes faith for me to believe that men walked on the moon in 1969. I’m convinced that it happened, but it doesn’t seem true to me. It doesn’t seem plausible that 1960′s technology could have accomplished this, even though I know that it did.
It takes faith for me to believe that Ernest Shackleton and his crew survived their exploration of the Antarctic. I don’t doubt the historical accounts, though they are hard to believe.
It takes faith for me to believe some mathematical theorems even though I have carefully gone through every line of their proofs. I am convinced that these theorems are true though they do not seem true. Other mathematicians have commented on the same experience. For example, Jerry Bona once joked that
The Axiom of Choice is obviously true; the Well Ordering Principle is obviously false; and who can tell about Zorn’s Lemma?
The three statements he mentions are logically equivalent, though the Axiom of Choice is the easiest to believe and the Well Ordering Principle is the hardest to believe.
It takes faith for me to believe in God. At times it doesn’t feel like God exists, though there are reasons to believe that He does. I have found these reasons convincing, and I hold on to my conclusions in spite of my changing moods.