One can go to work, do quality work for others, and be in service to other men and women every day. That is ministry. That kind of ministry is every bit as legitimate as what might be done in the confines of a church building. Now I don’t want to minimize the value of what good men and women do every day in church buildings all over the world as they seek to do good for others. Yet, neither do I want to minimize the value of one’s calling lived out in service to God.
Mark Roberts' review of God at Work addresses this same issue. His Appendix for the Laity (more here) is directed at helping disciples help their churches to help them live out their faith at work.