Biblical theology is the study of the story of the Bible as a whole. The Bible is not a collection of random, disconnected episodes; it tells the story of God’s progressive revelation throughout history. I find few people (including myself until relatively recently) have an understanding of this, and I believe understanding it will help a lot of believers and nonbelievers better understand the Christian faith.
Christians believe the Bible (and history) moves through 4 major events/eras:
At The Creation, God made the world good, but mankind (because he was given freewill) sinned and rebelled against God (The Fall). All creation was affected, and humankind was forever separated from an eternally good, holy God by their sin. God chose Israel as his special people and prepared them for the coming of Christ (the Messiah). Christians believe the whole Old Testament (OT) is preparing the world for the coming of Christ. (Many Jewish theologians would agree with this but disagree that Jesus is the Christ.)
Then, Jesus the Christ came, lived the sinless life that none of us could, and died for the sins of the world in our place (The Redemption). This puts into action The Restoration; people will be redeemed through Jesus Christ. This is where we are now in history, but the Restoration won’t reach fulfillment until Jesus’ Second Coming, at which time creation will be made right again. The phrase already/not yet is often used to speak of the time period we now live in within history; Jesus Christ has already started the Restoration, but the completion of the Restoration has not yet arrived.
What About Between the Fall and the Redemption?
Since the Creation and the Fall happened all within only the first 3 chapters of Genesis, and the Redemption doesn’t happen until Jesus’ life, the majority of the OT tells of the period between the Fall and Redemption, covering about 2,000 years once God appears to Abraham. (It’s unclear how much time passes during the earlier events recorded in Genesis to Abraham.) During these 2,000 years, God prepared Israel (and the world) for the Redemption, the coming of the Christ. As I said above, Christians understand all of the OT to point towards Jesus.
So, we’re in the Restoration. Now what?
Christians are commanded by Jesus Christ to spread the good news of his sacrificial love through words and actions so all can be redeemed from sin, to stay strong in their faith and be led by the Holy Spirit, and to wait. Wait for what? Jesus Christ’s Second Coming, when he will complete the Restoration with the final judgment and usher in the new heavens and new earth. The final destination of people who aren’t separated from God by sin will not be heaven, but the restored earth. Moreover, no new revelations from God, including new scriptures, are coming or are needed.