Why should expositional preaching include systematic theology?
Systematic theology is necessary in order to understand the text. When a text refers to God, or man, or sin, or Christ, or the church, or faith, you are in grave danger of distorting the meaning of those concepts unless you know what the whole Bible teaches about them—unless you know the Bible’s systematic theology. Also, without systematic theology you lack a crucial tool for defending against false interpretations of texts. In order to rightly interpret a verse in light of all of Scripture and defend a true interpretation against false ones you need systematic theology. Does Matthew 16 declare Peter to be the first pope? Well, that chapter does not say exactly. How you put together the rest of Scripture will affect how you then read Matthew 16 and answer that question.
Systematic theology is necessary in order to preach the gospel. Every expositional sermon should include the gospel because no text has been fully expounded unless it has been related to the gospel (through “biblical theology”). Yet in order to preach the full gospel you must preach what the Bible teaches about God’s holiness, our sin, Christ’s atoning death and resurrection, and our need to repent of sin and trust in Christ. Apart from a biblical summary of each of those things—that is, apart from systematic theology—none of those things make sense. Systematic theology is necessary in order to preach the gospel.
Systematic theology is necessary for spiritual growth. In order to grow in trusting God, a Christian needs to know what God is like. In order to grow in holiness, a Christian needs to understand the nature and offense of sin, as well as what God has done to save us from sin by sending Christ to die. This doesn’t mean that every Christian has to pore over thousand-page books, or even that every Christian has to understand the technical vocabulary of systematic theology. But it does mean that in order to grow spiritually every Christian needs to grow in his understanding of what the Bible teaches about God, sin, Christ, faith, and the duties of the Christian life. This comes through reading Scripture, synthesizing it, and applying it to our lives.
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