The church-centered means of grace: Preaching and sacraments
Sanctification in the Reformed faith is to be done through attending to the means of grace: preaching, sacraments, and prayer. The objective and church-based means are preaching and the sacraments. Thus, while prayer and striving to live a godly life are important, the main focus of Reformed piety is attending to the public means of grace in the corporate worship assembly on the Lord's Day.
Preaching is the authoritative proclamation of the truth of God's Word by God's servant to God's people. First of all, preaching is all about God's Word. Therefore, the content must be an exposition of Scripture. Biblical and Reformed preaching must be about expositing the Word of God and speaking only what the Word of God teaches. The preacher does not have any right to preach his own philosophy or his own ideas about what he thinks God's Word teaches. Neither does he have the right to change his message to make his hearers more comfortable. He also does not have the right to make the message "more practical." Where God's Word teaches doctrine, he must teach doctrine. Where God's Word teaches practical issues, he must be practical. Certainly, the preacher could and should show the practical implications of the text, but he has no right to make applications that are not derived from the text themselves.
Secondly, preaching is about the truth of God's Word. In other words, preaching must communicate truth that God's Word teaches. While it is true that Scripture covers many different genres, yet preaching is about exegeting the passage and proclaiming the truths in those passages. Preaching is not about just telling stories, even biblical narratives, but showing believers the truths God is conveying in the narratives, or in any poetry or any passage in any genre.
Thirdly, preaching is about the truth of God's Word, which imply that it is the truth of all of God's Word. This implies that the passage being exegeted and preached must be interpreted not just in its immediate context but also in its canonical context. That means that is must be interpreted in light of the progress of redemptive-history. Also, it must be interpreted in light of the central theme of covenants that is interwoven through the entire Scriptures. Last but not least, it must be interpreted through the framework of the Gospel, and therefore it must be interpreted through the lens of the Law and the Gospel, or the Covenant of Works and the Covenant of Grace.
Fourthly, preaching is done by God's servant. Therefore, it is to be done by someone called to the special office of a pastor/ teaching elder. Since there is nothing ontologically special about the pastor, therefore there is nothing to stop any man from taking the office, as long as he is qualified and called to that task. But he must be called to that task. While any believer can witness to others about the Gospel, and anyone can seek to teach and convince others of the truths of Scripture, only the pastor can proclaim the truth of God's Word in the context of a worship service.
Lastly, preaching is the authoritative proclamation of the truth of God's Word. According to the Scriptures, the pastor is a herald of God conveying God's truths to God's people (2 Cor. 5:20). The herald has the authority of the one who sends him, and therefore as God's herald, the message the pastor conveys is authoritative to the extent that it is a true interpretation and application of Scripture. Therefore, all preaching must be treated seriously. All believers must give heed to the preaching from the pulpit. Where the preacher preaches the Word of God, his message must be accepted and applied to one's life. Where the preacher deviates from God's truth, those parts are to be rejected and the preacher has to be reproved. Since the proclamation is authoritative, what is not allowable for any true believer to do is to treat it with indifference and apathy. Either the preacher preaches God's Word and must be obeyed, or he mixes in error with truth and the errors are to be explicitly rejected.
It is therefore noted that preaching in the Reformed tradition is different from much of modern Christianity. The emphasis on the text, the rejection of moralism, and the authoritative nature of the proclamation are all things the modern church downplays at best. In the Reformed church, a sermon is not a lecture or talk show performance. Believers who hear the Word preached are obligated to treat what the preacher proclaims seriously, and to ignore whatever is preached is sin.