So the men did as Joshua told them. They took twelve stones from the middle of the Jordan River, one for each tribe, just as the LORD had commanded Joshua. They carried them to the place where they camped for the night and constructed the memorial there. Joshua also built another memorial of twelve stones in the middle of the Jordan, at the place where the priests who carried the Ark of the Covenant were standing. The memorial remains there to this day. Joshua 4:8-9
Recently I experienced a great treat when two Messianic Jews, a husband-wife team from Israel, visited a local church to give their testimony and lead us through the Passover meal. They explained the symbolic meaning behind each of the Jewish customs in the meal that point to Jesus (all of them), which orthodox Jews totally miss. While they explained how the Bible ties the Passover to the coming Messiah between the Old and New Testaments, I will never forget what the wife said at one point:
"Churches and people get off the track when they don't keep the Old Testament and the New Testament together. They must be kept together to fully understand the truth."
I couldn't agree more, but unfortunately both Jews and many western Christians (the United States) haven't done this adequately. The Jews skip the NT, and most Christians skip the OT.
Why is this so important? What do we have to lose by not diving into the OT more, keeping it intact with our NT? The fact is, the OT bursts at the seams with The Story—the story of Jesus coming to die to save us from sin, so we could have everlasting life.
Now when I read my OT, it's like reading a great cosmic play with the Israelites in the starring role, acting out The Story preemptively. This was so that, a few thousand years later when Jesus came, their ancestors would be able to recognize their Messiah from the rich symbolism in the stories of old—stories God told them to "tell your children and grandchildren and never forget."
Case in point, check out the account of Joshua leading the Israelites across the Jordan into the Promised Land (further reading Joshua chapters 3-4). Plug these symbolic values into the equation for The Real Story that would take place 1,500 years later:
Joshua: He was a savior of the people and called a "Christ-type."
Israelites: Today, these are believers, both Jewish and Gentile.
Promised Land: The Kingdom and freedom from the bondage of sin and death.
Twelve Stones: Twelve Apostles—foundation stones of the church with Jesus as the chief cornerstone (Ephesians 2:20).
Middle of the Jordan: Where Jesus was baptized. Shortly after His baptism, He chose His 12 disciples just as the Israelites chose the 12 stones as a memorial.
Priests carrying the ark of the covenant: (I believe) The chosen servants of God carrying His presence to bring forgiveness, wholeness, and healing to the people.
And therein lies The Real Story. Personally, the more I keep the OT and the NT together, keeping in mind what's under the surface, the more intrigued, awed, and inspired I become about how this miraculous book—the Living Word of God—was put together over thousands of years with prophetic threads of The Real Story throughout.
Note: The very best way I know of to learn about The Story for yourself is to read the Bible through, cover to cover, yearly. You can do this with a regular Bible, a One Year Bible, or a Chronological Bible. I recommend NASB.