“The incomparably clearest sign in God’s providence is the fact that we have the neighbor we actually have. In that fact lies the law, an evidence of a definite vocation. Uncertainty as to whether one is called is often due to regarding oneself as an isolated individual, whose ‘call’ must come in some inward manner. But in reality we are always bound up in relations with other people; and these relations with our neighbors actually effect our vocation, since these external ties are made by God’s hands. A craftsman’s workshop is like a Bible, in which is written how he is to conduct himself toward his neighbor. Toos and food, needle and thimble — not even excepting ‘your beer-vat’ — call aloud, ‘Use us for the well-being of your neighbor!’ Things are the vehicle of the Word of God to us.”
This is Luther, according to Gustaf Wingren in Luther on Vocation.