"Read the divine scriptures constantly; never, indeed, let the sacred volume be out of your hand. Learn what you have to teach. “Hold fast the faithful word as you have been taught that you may be able by sound doctrine to exhort and convince the gainsayers. Continue thou in the things that thou hast learned and hast been assured of, knowing of whom thou hast learned them;” and “be ready always to give an answer to every man that asketh you a reason of the hope and faith that are in you.” Do not let your deeds belie your words; lest when you speak in church someone may mentally reply “Why do you not practise what you profess? Here is a lover of dainties turned censor! his stomach is full and he reads us a homily on fasting. As well might a robber accuse others of covetousness.” In a priest of Christ mouth mind, and hand should be at one."
Jerome Letters 52.7