These and other things both the priest ought to know in order to teach, and the people to believe in order that they may understand what they are taught; as the Apostle says: Unless you believe, you shall not understand (Isa. 7:9, according to the Septuagint). Whence it is given to understand that understanding does not arise from faith out of intellect, but intellect out of faith; nor does he who understands believe, but he who believes understands, and he who has understood acts well; as it is written elsewhere: He would not understand, that he might act well (Ps. 35:4). It did not say: He could not, but he would not understand; so that we may recognize that to be unwilling to understand is nothing other than to be unwilling to believe; and therefore, that one may act well, let him strive to understand, and that he may understand, let him believe. But since the same Apostle says: Faith comes by hearing;
and hearing comes through the word of God (Rom. 10:17), the teacher of the Church ought to preach what the one about to believe may hear: for without preaching there will be no hearing; the same Apostle attesting and saying: How shall they hear without a preacher (ibid., 14)? If, therefore, anyone without a preacher does not hear, without hearing does not believe, without faith does not understand, without understanding does not act well; the word of faith must be preached, that hearing he may believe, believing understand, and understanding persevere in good work: for, since one who is able to use the choice of free will, neither works without faith nor faith alone without works justifies. And therefore, if with the heart one believes unto righteousness, but with the mouth confession is made unto salvation;