“All doubt is cowardice — all trust is brave.”
“To have doubted one's own first principles is the mark of a civilized man.”
“What is clear to one man may be doubtful to another.”
“The doubtful beam long nods from side to side.”
“Those who do not doubt do not believe. Faith is maintained by resolving doubts, and again resolving those further doubts which are suggested by the resolution of previous doubts.”
“People, when asked if they are Christians, give some of the strangest answers you ever heard. Some will say if you ask them: "Well — well — well, I, — I hope I am." Suppose a man should ask me if I am an American. Would I say: "Well, I — well, I — I hope I am?"”
Quotes via Wikiquote (CC BY-SA), each with its original source.