“Let those who believe, believe. Let those who doubt, doubt.”

“Believe those who are seeking the truth. Doubt those who find it.”

“People must believe what they can, and those who believe more must not be hard upon those who believe less. I doubt if you would have believed it all yourself if you hadn't seen some of it.”

“Beliefs are the foundation of actions. Those who believed without doubting, he would say, acted without thinking. And those who acted without thinking were enslaved.”

“Those who believe they believe in God, but without passion in the heart, without anguish of mind, without uncertainty, without doubt, and even at times without despair, believe only in the idea of God, and not in God himself.”

“Those who believe that they believe in God, but without passion in their hearts, without anguish in mind, without uncertainty, without doubt, without an element of despair even in their consolation, believe only in the God idea, not God Himself.”