The core and center of the Scriptures is the person of Jesus. All that the Old Testament conveys points us to him. The Old Testament is more than a series of specific prophecies that find their fulfillment in the person of Jesus, with everything else simply "filler." All of the Old Testament, just as the New, is focused on him. He is "Israel reduced to one." The offices of Christ-Prophet, Priest and King-are understandable only in light of the Old Testament offices. Conversely, the Old Testament offices are understandable only in light of the incarnation. Everything that took place before the incarnation is focused on him as much as everything that has happened since or will happen in the future is focused on him.
The continuity of the two testaments, and the continuity of the ongoing people of God, is all about Jesus. Reading the Old Testament is reading the word of Jesus who spoke by the prophets. He connects the history of ancient Israel with modern Israel, the church. From Genesis to Revelation, there is one narrative, one story, one Scripture. Marcion erred not just in the breadth of his de-canonization of the entire Old Testament but in his de-canonization of any of it. If the church is to be faithful to her own understanding of the Scriptures as the only source and norm for faith and life, the Old Testament must be an equal partner to the New Testament. For, indeed, they are not two but one Scripture, united in their witness to Christ.
As can be seen with some scholars today, there is a tendency to reduce the canon to a "canon within a canon." Parts of the OT become subordinate to the NT and thus the unity of the Scriptures is dismantled. Dr. Gard's article is worth reading in light of this current trend.