In my blog post on Willow Creek, I said that many Reformed evangelicals think of sound, expository preaching as something of a 'magic bullet.' We may think that as long as we are preaching the Word--preaching the law and the gospel rightly--that everything else in congregational life will somehow take care of itself. We may give lip service to the other two marks of the church--the administration of the sacraments and discipline--but we don't give them proper weight. Fully considered, the administration of the sacraments includes pastoral care, education, and discipleship, while the ministry of discipline means rightly ordering the community, that is, pastoral leadership.
I have often seen many men spend a great amount of time on preparing and preaching lengthy, dense, expository messages, while giving far less time and energy to the learning of leadership and pastoral nurture. It takes lots of experience and effort to help a body of people make a unified decision, or to regularly raise up new lay leaders, or to motivate and engage your people in evangelism, or to think strategically about the stewardship of your people's spiritual gifts, or even to discern what they are. It takes lots of experience and effort to know how to help a sufferer without being either too passive or too directive, or to know when to confront a doubter and when to just listen patiently. Pastors in many of our Reformed churches do not seem to be as energized to learn to be great leaders and shepherds, but rather have more of an eye to being great teachers and preachers.
I'd point us to the example of John Calvin himself. No one put more emphasis on expository preaching as central to ministry. And yet Calvin sat nearly every Thursday in the Consistory, hearing hundreds of practical pastoral cases each year brought by the elders of the city to the council of pastors and other elders. He applied his theology to the intimate details of "adultery and fornication, disputed engagements and weddings, family quarrels, incest, rape, sodomy, buggery, prostitution, voyeurism, abortion, child neglect, child abuse, education disputes, spousal abuse, mistreatment of maids, family poverty, embezzlement of family property, sickness, divorce, marital property disputes, inheritance..." (Witte and Kingdon, Sex, Marriage, and Family in John Calvin's Geneva, Vol 1, p. 15.) Also, Calvin's voluminous correspondence shows what a forceful and wise leader and statesman he was. Because Calvin was not only a preacher but also a great shepherd and leader, he built up the church in a way that changed the world.
I pastor a church with a large staff and so I give 15+ hours a week to preparing the sermon. I would not advise younger ministers to spend so much time, however. When I was a pastor without a staff I put in 6-8 hours on a sermon. If you put in too much time in your study on your sermon you put in too little time being out with people as a shepherd and a leader. Ironically, this will make you a poorer preacher. It is only through doing people-work that you become the preacher you need to be--someone who knows sin, how the heart works, what people's struggles are, and so on. Pastoral care and leadership (along with private prayer) are to a great degree sermon preparation. More accurately, it is preparing the preacher, not just the sermon. Through pastoral care and leadership you grow from being a Bible commentator into a flesh and blood preacher.