Gene Edward Veith, Jr. explains the Reformation doctrine of vocation:
“When we pray the Lord’s Prayer, observed Luther, we ask God to give us this day our daily bread. And He does give us our daily bread. He does it by means of the farmer who planted and harvested the grain, the baker who made the flour into bread, the person who prepared our meal. We might today add the truck drivers who hauled the produce, the factory workers in the food processing plant, the warehouse men, the wholesale distributors, the stock boys, the lady at the checkout counter. Also playing their part are the bankers, futures investors, advertisers, lawyers, agricultural scientists, mechanical engineers, and every other player in the nation’s economic system. All of these were instrumental in enabling you to eat your morning bread.
Before you ate, you probably gave thanks to God for your food, as is fitting. He is caring for your physical needs, as with every other kind of need you have, preserving your life through His gifts. “He provides food for those who fear him” (Psalm 111:5); also to those who do not fear Him, “to all flesh” (136:25). And He does so by using other human beings. It is still God who is responsible for giving us our daily bread. Though He could give it to us directly, by a miraculous provision, as He once did for the children of Israel when He fed them daily with manna, God has chosen to work through human beings, who, in their different capacities and according to their different talents, serve each other. This is the doctrine of vocation.”
Gene Edward Veith Jr., God at Work: Your Christian Vocation in All of Life, Illinois:Crossway, 2002, pages 13-14.