David Murray has put together a great list of reasons to study your Old Testament. Often times in our Bible study, we miss the forest for the trees. We focus so much on the immediate context (which as a firm adherent to dispensationalism, I appreciate) that we neglect the overarching storyline of the Bible.
Being faithful to the Scriptures takes work--hard work. Let's move beyond using the Old Testament as a Christian Aesop's Fables, and remember that the whole book testifies of Christ. If you have left Jesus out, you've missed the point.
7. The Old Testament makes you appreciate the New Testament more.
For all the Old Testament reveals of Jesus, and of Christian doctrine and experience, we must concede that it also conceals, that there’s a lot of frustrating shadow, that there’s unfulfilled longing and desire, that there’s often something—or rather someone—missing. The more we read it, the more we long for and love the incarnate Christ of the New Testament. The dawn is beautiful, but the sunrise is stunning.