Is the Old Testament still important if we emphasize Paul's epistles?
Yes. Emphasizing Paul's epistles never means forgetting the rest of Scripture. The Old Testament is just as well fitted as the New, and everything in the Old dovetails with the New. It belonged predominantly to Israel's law economy, while Paul reveals God's mystery for today.
Les explains that although he emphasizes Pauline teaching and thinks 90% of Bible reading and study should be in Paul's epistles, he never indicates that believers should forget the rest of Scripture. The Old Testament is just as well fitted as the New, and all Scripture dovetails together. The Old Testament operated predominantly under the economy of law to the nation of Israel, with its temple worship, priesthood, and sacrifices. Now that God has turned to the Gentile, that economy had to slip off the scene, and something totally different exists. The language found in Romans and Paul's other epistles—the mystery now revealed—is not found in the Gospels or the Old Testament because it was held in the mind of God and is now being revealed.