5 And in the first place it is clear that the more important, complex and difficult an office is the longer and more careful should be the preparation undergone by those who are called to fill it. But is there on earth a dignity higher than that of the priesthood or a ministry imposing a heavier responsibility than that whose object is the sanctification of all the free acts of man? Is it not of the government of souls that the Fathers have rightly said that it is "the art of arts;" that is, the most important and most delicate of all tasks to which a man may be applied for the benefit of his kind? - "Ars artium regimen animarum?"(3) Nothing must then be neglected to prepare those whom a divine vocation calls to this mission in order that they may fulfill it worthily and fruitfully.
Source: Depuis le Jour (Vatican.va)