Faith is a reasoning trust, a trust which reckons thoughtfully and confidently upon the trustworthiness of God.—John Stott (b. 1921)

Doubt isn’t the opposite of faith; it is an element of faith.―Paul Tillich (1886–1965)

Doubts are the ants in the pants of faith. They keep it awake and moving.―Frederick Buechner (b. 1926)

The relationship between commitment and doubt is by no means an antagonistic one. Commitment is healthiest when it is not without doubt, but in spite of doubt.―Rollo May (1909–1994)

Sometimes doubting is not a lack of faith, but an expression of it. Sometimes to doubt is to merely insist that God be taken seriously not frivolously, to insist that our faith is placed in and upheld by something other than seeming conjuring tricks.―Mark Buchanan (b. 1960) 

For many people in our world, the opposite of faith is doubt. The goal, then, within this understanding, is to eliminate doubt. But faith and doubt aren’t opposites. Doubt is often a sign that your faith has a pulse, that it’s alive and well and exploring and searching. Faith and doubt … are, it turns out, excellent dance partners.―Rob Bell (b. 1970)

I think there is no suffering greater than what is caused by the doubts of those who want to believe. I know what torment this is, but I can only see it, in myself anyway, as the process by which faith is deepened. A faith that just accepts is a child’s faith and all right for children, but eventually you have to grow religiously as every other way. … If you feel you can’t believe, you must at least do this: keep an open mind. Keep it open toward faith, keep wanting it, keep asking for it, and leave the rest to God.―Flannery O’Connor (1925–1964) 

The great leaders of the people of God, like Moses, have always left room for doubt. You must leave room for the Lord, not for our certainties; we must be humble.—Pope Francis (b. 1936)

You can’t stand effectively on “blind” faith. You must have a “knowing” faith, and that comes from believing wholeheartedly what the Word promises. You know God has spoken it and declared it to be so, and you know you can depend on that.—Gloria Copeland (b. 1942)

For many of us, the great danger is not that we will renounce our faith. It is that we will become so distracted and rushed and preoccupied that we will settle for a mediocre version of it.—John Ortberg (b. 1957)