If thou hast not understood, said I, believe. For understanding is the reward of faith. Therefore do not seek to understand in order to believe, but believe that thou mayest understand; since, “except ye believe, ye shall not understand.”

Therefore when I would counsel the obedience of believing toward the possibility of understanding, and say that our Lord Jesus Christ has added this very thing in the following sentence, we find Him to have said, “If any man be willing to do His will, he shall know of the doctrine” (John 7:17). What is “he shall know”? It is the same thing as “he shall understand.” But what is “If any man be willing to do His will”? It is the same thing as to believe.

—Augustine
NPNF 7:184–185.