From the writings of st Josemaria:
http://www.escrivaworks.org/book/friends_of_god/point/60
Forgive this digression and, though we haven't really gone off the track, let us return to the central idea. Be convinced that our professional vocation is an essential and inseparable part of our condition as Christians. Our Lord wants you to be holy in the place where you are, in the job you have chosen for whatever reason. To me, every job that is not opposed to the divine law is good and noble, and capable of being raised to the supernatural plane, that is, inserted into the constant flow of Love which defines the life of a child of God.
I cannot avoid getting a little uneasy when someone, in speaking about his job, plays the role of a victim. He talks about how his work takes up so many hours each day, when the truth is that he isn't doing half as much as many of his professional colleagues are and they quite likely are only driven by selfish or, at best, by merely human motives. All of us who are here engaged in a personal dialogue with Jesus have very definite occupations: doctors, lawyers, economists... Think a moment about those of your colleagues who are outstanding for their professional prestige, their integrity or their spirit of service and self-sacrifice. Isn't it true that they devote many hours of the day, and even of the night, to their jobs? Isn't there anything we can learn from them?
While I speak, I too am examining the way I have behaved and I confess that, in putting the question to myself, I feel a little ashamed and wish immediately to ask God's forgiveness, thinking how weak my response has been and how far short it has fallen of the mission that God has given us to carry out in the world. One of the Fathers of the Church writes: 'Christ has appointed us to be like lamps, so as to be teachers to others; to act as leaven; to live like angels among men, like adults among children, like spiritual beings among the merely rational; to be seed and to yield fruit. There would be no need of speaking if our lives shone in this way. Words would be superfluous if we had deeds to show for them. There would not be a single pagan left if we were truly Christian.'
We must avoid the error of thinking we can reduce the apostolate to the performance of a few pious practices. You and I are Christians but at the same time, and without any break in continuity, we are citizens and workers with clear obligations, which we have to fulfil in an exemplary manner if we really want to become saints. Jesus himself is urging us: 'You are the light of the world. A city set on a mountain cannot be hidden. Neither do men light a lamp and put it under a measure, but upon the lampstand, so as to give light to all in the house. Even so, let your light shine before men, in order that they may see your good works and give glory to your Father in heaven.'
Professional work, whatever it is, becomes a lamp to enlighten your colleagues and friends. That is why I usually tell those who become members of Opus Dei, and the same applies to all of you now listening to me: 'What use is it telling me that so and so is a good son of mine a good Christian but a bad shoemaker?' If he doesn't try to learn his trade well, or doesn't give his full attention to it, he won't be able to sanctify it or offer it to Our Lord. The sanctification of ordinary work is, as it were, the hinge of true spirituality for people who, like us, have decided to come close to God while being at the same time fully involved in temporal affairs.
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