Gregory the Great, in his book, Pastoral Care (written in AD 590), speaks well to the importance of training for the significant task of guarding and guiding souls.

“No one ventured to teach any art unless he has learned it after deep thought. With what rashness, then, would the pastoral office be undertaken by the unfit, seeing that the government of souls is the art of arts! For who does not realize that the wounds of the mind are more hidden than the internal wounds of the body? Yet, although those who have no knowledge of the powers of drugs shrink from giving themselves out as physicians of the flesh, people who are utterly ignorant of spiritual precepts are often not afraid of professing themselves to be physicians of the heart, and though, by divine ordinance, those now in the highest positions are disposed to show a regard for religion, some there are who aspire to glory and esteem by an outward show of authority within the holy Church.” p.22

(I previously gave an overview of this book here)