If someone desires to have peace in this life, as well as eternal happiness, he must find it in religion. Since the fall of man, the only true religion is that which has been revealed by God. He has revealed this truth, bit by bit, in different ways, gradually building until the arrival of Jesus Christ (Hebrews 1:1-2), in whom all treasures of wisdom and knowledge are hidden (Colossians 2:3). In Christ alone, God’s grace is perfectly revealed. According to His eternal plan, God has laid out history in such a way that Christ is the central focus of all His dealings with mankind, with all revelation ultimately pointing to His work on the cross, and eventually to His final return at the second coming, when all things will be brought together in Him. Because of this, we ought to always be looking for Christ in the Scriptures, trying to discern what the text is saying about Him. The Holy Spirit speaking in the New Testament provides the most clear explanation of God’s glory in Christ, by showing us new heights of grace and love that previous generations had never seen. Thus, in order to best understand the Old Testament, we must view it through the lens of the New.
However, just because the New Testament is a clearer revelation, it does not mean that the Old Testament is no longer useful! Quite the opposite, we should take the time to seriously study the Old Testament, because in order to thoroughly understand the gospel of grace, we must first understand God’s law, and the historical background of God’s creation and progressive dealings with mankind. The Old and New Testaments are so dependent upon each other that neither can be understood by itself. If we are to have a complete system of truth, we need God’s complete set of written revelation: the 66 books of the Bible (II Timothy 3:16-17).
[See Nehemiah Coxe, Covenant Theology: From Adam to Christ, pp. 33-34.]