Blog 75: 2.11.4 - 2.11.9
Although the unity of the old and new covenants is primary, the differences between the two covenants are also important.
The first of these differences, as we have seen, concerns the manner in which eternal benefits are experienced, whether first by tasting a related blessing on earth (the Old Testament), or simply by exercising faith in a future inheritance (the New Testament).
A second difference between the Old and New Testaments relates to the use of various figures that typify Christ. Whereas the Old Testament often uses shadows and images to portray the gospel, the New Testament "reveals the very substance of truth as present" (II.xi.4).
The book of the Bible that teaches this principle most clearly is Hebrews, where the priesthood of the Old Testament is connected to the priestly ministry of Jesus Christ. His priesthood is superior in every way: in its permanency, in the perfection of its sacrifice, and in the holiness it brings to sinners. By comparison, the Old Testament priesthood was merely a "shadow of good things to come" (Heb. 10:1).
A third difference between the Old and New Testaments is that whereas the former is literal, the doctrine of the latter is spiritual. Calvin finds this teaching its classic location: Jeremiah's promise of a new covenant that will be written on the hearts of God's people. He also finds it in 2 Corinthians 3, where the apostle Paul distinguishes between the death that the law brings by revealing unrighteousness and the life that the gospel offers by giving us the righteousness of Christ.
Then there is a fourth, closely-related difference between the two testaments. The Old Testament, with its law, keeps sinners in bondage to fear, but the New Testament, with its gospel, offers sinners freedom in Christ.