Bottom line: Fulfilled prophecy gives us assurance that prophecies yet fulfilled will be fulfilled.
Daniel 7 records Daniel's vision of strange beasts and a coming King. Daniel sees four world empires (Babylon, Medo Persia, Greece, and Rome) rise onto the scene in succession. And he ultimately sees the coming Kingdom of Jesus and His coronation as King.
Daniel 7 is perhaps the most important chapter in the book. It is what we call a primary reference. That means it contains original prophecy that will be quoted and referenced by others such as Jesus, Paul, and John the Revelator. In this one chapter, God's incredible, unchangeable redemptive plan for human history is laid out.