Later this weekend I will post my summary thoughts on "The Christian and Work," which really reflects the Reformed understanding of vocation. For now, here are some good words from Alister McGrath.
God calls his people, not just to faith, but to express that faith in quite definite areas of life. Whereas monastic spirituality regarded vocation as a calling out of the world into the desert or the monastery, Luther and Calvin regarded vocation as a calling into the everyday world. The idea of a calling or vocation is first and foremost about being called by God, to serve Him within his world. Work was thus seen as an activity by which Christians could deepen their faith, leading it on to new qualities of commitment to God. Activity within the world, motivated, informed, and sanctioned by Christian faith, was the supreme means by which the believer could demonstrate his or her commitment and thankfulness to God. To do anything for God, and to do it well, was the fundamental hallmark of authentic Christian faith. Diligence and dedication in one’s everyday life are, Calvin thought, a proper response to God.
... The work of believers is thus seen to possess a significance that goes far beyond the visible results of that work. It is the person working, as much as the resulting work, that is significant to God. There is no distinction between spiritual and temporal, sacred and secular work. All human work, however lowly, is capable of glorifying God. Work is, quite simply, an act of praise-a potentially productive act of praise. Work glorifies God, it serves the common good, and it is something through which human creativity can express itself. The last two, it must be stressed, are embraced by the first. As Calvin’s English follower William Perkins put it, "The true end of our lives is to do service to God in serving of man." - Alister McGrath, Calvin and the Christian Calling in First Things