I would offer two main principles in answer to the question, “Why should we preach Christ in every sermon?”: (1) Biblical Hermeneutics, and (2) Biblical Example.
1. Biblical hermeneutics requires us to preach Christ in every sermon. The historical rise of literal-grammatical-historical hermeneutics in the history of interpretation has been a very good thing. There is general agreement among evangelical teachers that the Bible should be taken literally (unless it uses metaphor, typology, allegory, parable, etc.), grammatically (using the original languages for exegesis), and historically (dealing with the historical context of the text). As part of this method, we also include the idea of the “analogy of Scripture” (Analogia Scripturae), which refers to the Scripture interpreting the Scripture. This is the foundation of exegeting a text and then expositing it in the sermon and is intended to prevent eisegesis (reading into the text) in order to be faithful to God’s specific Word. Sometimes, this principle is used to justify excluding the proclamation of Christ in a sermon, if He is not mentioned specifically in the text, especially when expounding an Old Testament text.
However, grammatical-historical exegesis is not the complete hermeneutical method used by Reformed interpreters or by historic Baptist interpreters. Reformed hermeneutics involves grammatical-historical-theological exegesis. The addition of “theological exegesis” for each text is sometimes called “scopus Scripturae.” It means that the exegesis of each text must look at the full theological context in which it resides; i. e., the place in biblical history, the covenant context in which it resides, and its relationship to the overall theology of the Scripture with Christ at the center. This means that the overall theology of Scripture, which is Christ-centered, must be included in the full exegesis of the text. This is not eisegesis. It is theological exegesis.
William Ames, an important theologian for early Baptists, said, “The Old and New Testaments are reducible to these two primary heads. The Old promises Christ to come and the New testifies that he has come.” John Owen, another important Puritan theologian to early Baptists, said, “Christ is . . . the principal end of the whole of Scripture….” Nehemiah Coxe, pastor of the Petty France Baptist Church, and one of the authors of the Second London Confession, wrote, “…in all our search after the mind of God in the Holy Scriptures we are to manage our inquiries with reference to Christ.”
This theological element in hermeneutics is not the same as the “Analogy of Scripture,” or “Scripture interpreting Scripture.” An exegete may use cross-reference or word-studies of a text, comparing Scripture with Scripture and still miss the overall theology of Scripture in the exegesis. The “scope of Scripture” (Scopus Scripturae) takes the whole counsel of God into account, the faith once-for-all delivered to the saints, when interpreting the text. For instance, when preaching on an Old Testament text, one may use the literal-grammatical-historical method, including Scripture interpreting Scripture in cross-references and word-studies, expounding the text faithfully in its original meaning in the Old Testament. Our Lord, however, explained that He came to fulfill the Law and the Prophets. To explain the Old Testament text and to expound its original contextual meaning without taking into account how our Lord fulfilled it in His person and work ignores the full theological interpretation of the text.
To preach Christ in every sermon is more than just preaching a text in its literal-grammatical-historical meaning and then launching into an unconnected explanation of the gospel. Rather, preaching Christ is explaining how each text is connected to and fulfilled theologically in Jesus Christ, the theological center of God’s revelation to man. This hermeneutical principle does not demean the Old Testament as less inspired or not as important as the New Testament. Rather, it recognizes that every Old Testament text reaches its full meaning in the revelation of Jesus Christ in all the Scriptures.
One more thing about the theological principle of interpretation. It recognizes that all men are born condemned under law in the fall of Adam, and that from Gen. 3:15 on, the whole of Scripture reveals the coming of Christ under grace. This is the old Law and Gospel theology that was central to the Reformation’s rediscovery of the gospel. All of Scripture must be interpreted in light of the Law/Gospel theology which reveals Jesus Christ to man. This enables the expositor to preach the gospel in every sermon legitimately without eisegesis. Charles Bridges, in The Christian Ministry, said:
The mark of a minister “approved unto God, a workman that needeth not to be ashamed,” is, that he “rightly divides the word of truth.” This implies a full and direct application of the Gospel to the mass of his unconverted hearers, combined with a body of spiritual instruction to the several classes of Christians. His system will be marked by Scriptural symmetry and comprehensiveness. It will embrace the whole revelation of God, in in its doctrinal instructions, experimental privileges, and practical results. This revelation is divided into two parts–the Law and the Gospel–essentially distinct from each other, though so intimately connected, that an accurate knowledge of neither can be obtained without the other (222).
2. Biblical example requires us to preach Christ in every sermon. We now live under the New Covenant of Jesus Christ, the completed revelation of God to man. We have been given the full revelation of God in the faith once-for-all delivered to the saints. Our example of preaching and teaching is now displayed in how Christ and His Apostles preached and taught. His teaching of Himself, each sermon in Acts to unbelievers, and each Epistle to believers is fully Christ-centered. When we take a text from Christ or the Apostles’ writings which do not explicitly mention the Lord Jesus Christ, we must explain them in light of their whole teaching in the context of His message and the whole epistle’s message. These are our examples of biblical preaching under the New Covenant.
For modern-day examples of such preaching, you only have to look at the greatest preacher of the 19th century, Charles Spurgeon, and the greatest preacher of the 20th century, Martyn Lloyd-Jones. They both followed the grammatical-historical-theological method of hermeneutics to preach Christ in all the Scriptures.