"The ultimate irony of faith is that it necessarily admits doubt. It is the belief in things not seen. It is beyond our capacity as human beings to know with certainty what God has planned for us or what He asks of us, and those of us who believe must trust that His wisdom is greater than our own. This doubt should not push us away from our faith. But it should humble us. It should temper our passions, and cause us to be wary of self-righteousness."

President Obama, speaking at Notre Dame commencement.