Biblical theology is necessary in order to understand the text. We can truly understand a text of Scripture only by situating it within the overall narrative of redemptive history.
Biblical theology is necessary in order to apply the text. In order to understand how passages from Leviticus or the Psalms or Amos or Acts apply to Christians today, we need to understand the continuities and discontinuities between the text’s place in redemptive history and ours. For instance, if you’re preaching from Leviticus, you need to teach your people that Christ’s death on the cross fulfilled the entire Levitical system and rendered it obsolete (see Hebrews 8-10) in order for them to understand how a passage from that book applies to their lives.
Biblical theology enables you to preach the gospel from every passage of Scripture. One biblically sound way to preach the gospel in every sermon is to relate the text to the overall narrative of Scripture, the center of which is the saving death and resurrection of Christ.
Biblical theology is necessary in order to explain how the Bible fits together. By showing how different portions of the Bible relate to the others, biblical theology enables Christians to understand the Bible as a coherent whole.
Biblical theology strengthens Christians’ confidence in the unity and truthfulness of Scripture. By demonstrating how God keeps his promises, how prophesies have been fulfilled, and how all the Old Testament points forward to the work of Christ, biblical theology strengthens Christians’ confidence in the unity and truthfulness of Scripture.
Biblical theology inspires and encourages Christians. When Christians understand the sweeping grandeur of God’s saving purposes they will be inspired to worship God and encouraged to persevere in faith.