How can I know I'm doing what God wants me to do? The answer is less esoteric or difficult than many would suspect: if you're seeking in everything to glorify God, you're doing what He wants you to do. Too often we think we're only really serving God if we're explicitly working in His service through evangelism, missions, teaching, etc., but the truth is much simpler. God puts us in a specific context so that we might bear witness of Him.
In the Lord's Prayer we ask God to give us our daily bread. Martin Luther affirmed that God does give us our daily bread, but that He does so by means of the farmer, baker, and grocer through whom we receive our loaves. This is the foundation for Gene Veith's book God at Work: Your Christian Vocation in All of Life, an exploration of the biblical doctrine of vocation, how it applies to those of us in a modern context, and how we can make the most of our God-given context.
There are many important distinctions in this book. One of the most essential is that between grace and works—while we trust our salvation is through no work at all on our part, we also realize that good works are the fruit of such faith. God doesn't need our good works, but our neighbor does, and we supply our neighbor with good works primarily through our vocation, whether your vocation is that of musician, plumber, or housewife.
Veith also discusses the way modern society has drained the very word "vocation" of all its theological meaning. As a result, we think of vocation strictly in terms of our secular employment, not taking into account the fact that each of us has many professions: at work, in the home, in the community, at church. Fatherhood is as much a vocation as engineering, and playing the piano for Sunday morning worship is just as vocational as caring for three children.
This book should be made essential reading for every Christian, especially those believers who struggle with feelings of inferiority or inadequacy because they aren't devoting their whole lives explicitly to spiritual work. Veith illuminates the Reformation doctrine of vocation, showing us that it is nothing more or less than doing everything for the glory of God, and encouraging each of us to rest in the finished work of Christ even as we pursue the good works He created for us to do.