In his book, A Quest for Godliness: The Puritan Vision of the Christian Life, author J.I. Packer writes about the centrality and importance of preaching in the process of sanctification. In fact, the Puritan pastor believed they would “never perform a more important task than preaching.”  While it has become “our habit to think of pastoral work as a matter of visiting and personal dealing only, and to oppose it to the public preaching of the Word; a man, we say, may be a bad preacher but a good pastor; but to the Puritan, faithful preaching was the basic ingredient in faithful pastoring.” 
While it must be emphasized that all believers are ministers (i.e., those who have received spiritual gifts to use in service to others), not all are ministers of the Word in the unique sense of the pastoral calling.
Choosing a luminary among the Puritans, Packer cites none other than John Owen, who said,
“The first and principal duty of a pastor is to feed the flock by diligent preaching of the Word… According to the example of the apostles, [pastors] are to free themselves from all encumbrances, that they may give themselves wholly unto the Word and prayer.” 
According to the Puritans (and I would suggest the Scriptures as well), if you are a pastor, your primary calling is to expound clearly the gospel of Jesus from the Scriptures, teaching expositorily, with spiritual unction and application.
In other words, your primary pastoral work is preaching work. God will grow your people in maturity, and through your teaching, give the opportunity to make personal application to congregant’s particular needs when those needs become apparent through the conviction of the Holy Spirit.
The Apostle Paul knew, with all of the potential distractions facing the pastor’s preparation and delivery of sermons, that his pastoral protege, Timothy, would be tempted to neglect the hard work of sermon preparation, since it requires time and solitude and a potential neglect of the expected visitation ministry people might expect. To this temptation, Paul charged Timothy,
“1 In the presence of God and of Christ Jesus, who will judge the living and the dead, and in view of his appearing and his kingdom, I give you this charge: 2 Preach the word; be prepared in season and out of season; correct, rebuke and encourage—with great patience and careful instruction. 3 For the time will come when people will not put up with sound doctrine. Instead, to suit their own desires, they will gather around them a great number of teachers to say what their itching ears want to hear. 4 They will turn their ears away from the truth and turn aside to myths.” 
Timothy was to commit himself to a full-orbed, doctrinally sound, Christ-centered preaching ministry. Why? This is what God’s people need. What churches need from their pastors is the Word preached over and over and over, because faith comes (and increases) by hearing the Word.  And preaching preparation takes time. It takes mental energy. It must be the devoted focus of the pastor… for the good of the church.
So preachers, be encouraged to give yourself to this glorious calling! Feed the sheep with the nutritious substance of God’s Word, expounding the Scriptures, centering on the person and work of Jesus. This is the best job in the world.
 J.I. Packer, A Quest for Godliness, 282.
 Ibid., 282.
 Ibid., 283.
 John Owen, Works, XVI:74f. Quoted in Quest for Godliness, 283.
 2 Timothy 4:1-4
 Romans 10:17, “Consequently, faith comes from hearing the message, and the message is heard through the word about Christ.”