8 Others may think what they like and follow each his own bent. But to me a town is a prison and solitude paradise. Why do we long for the bustle of cities, we whose very name speaks of loneliness? To fit him for the leadership of the Jewish people Moses was trained for forty years in the wilderness; and it was not till after these that the shepherd of sheep became a shepherd of men. The apostles were fishers on lake Gennesaret before they became “fishers of men.” But at the Lord's call they forsook all that they had, father, net, and ship, and bore their cross daily without so much as a rod in their hands.
I say these things that, in case you desire to enter the ranks of the clergy, you may learn what you must afterwards teach, that you may offer a reasonable sacrifice to Christ, that you may not think yourself a finished soldier while still a raw recruit, or suppose yourself a master while you are as yet only a learner. It does not become one of my humble abilities to pass judgment upon the clergy or to speak to the discredit of those who are ministers in the churches. They have their own rank and station and must keep it. If ever you become one of them my published letter to Nepotian will teach you the mode of life suitable to you in that vocation. At present I am dealing with the forming and training of a monk; of one too who has put the yoke of Christ upon his neck after receiving a liberal education in his younger days.
Source: Letters (New Advent)