Biblical theology teaches a Christian to understand his or her own story in light of God’s story. When a Christian understands that God is sovereign over all of history and has been working out one sweeping plan of salvation for thousands of years, it helps put his own story in perspective.
Biblical theology teaches a Christian where he’s from and where he’s going. Biblical theology puts together the whole story of the Bible, from creation to the new creation. When a Christian understands that he began in sin like the rest of humankind but is now headed toward an eternity of joyful fellowship with God and God’s people it will inspire endurance, hope, and joy in the midst of struggles.
Biblical theology teaches a Christian how the whole Bible fits together. If you just drop into a book in the Bible without knowing where it’s set in redemptive history you’re likely to become confused and discouraged. But biblical theology helps Christians understand how the whole Bible fits together, which illumines our understanding of each individual part.
Biblical theology teaches a Christian how to apply all the different parts of the Bible to his or her life. What on earth do Levitical sacrifices have to do with a Christian? What about the Israelite conquest of Canaan? Or the kingship of David and Solomon? Biblical theology helps Christians understand all of these portions of Scripture in light of the work of Christ to which they point, and it helps Christians see how they are relevant for their lives today.