There is discipline in labor. The scrupulous performance of work of any kind improves both the mind and the heart. A thorough and punctual mechanic is a man of character. He possesses a mental solidity and strength that render him a noticeable man and a reliable man in his sphere. The habit of doing work uniformly well, and uniformly in time, is one of the best kinds of discipline. He who has no profession or occupation must be, and as a matter of fact is, an undisciplined man. And in case one has an occupation or profession, the excellence of his discipline is proportioned to the fidelity with which he follows it. If he half does his work, his moral character suffers. If he does his work thoroughly, when he does it at all, but does not perform it with punctuality and uniformity (a thing which is, however, not likely to happen), it is in expense of his moral power.
(p 296 of Homiletics and Pastoral Theology)