What is the plan of salvation and what are the differences and changes in the Old and the New Covenants?
Now, in a sense the term "old" and "new" covenant are both accurate and inaccurate. They are both one and the same covenant- it is the ‘old people’ and the ‘new people’ that constitute the old and the new, Israel the people, is the old covenant, and the Christian community is the new people of the covenant. It is the same God and the same covenant, and Paul uses the image of a vine with the old cut out and the new grafted in. So the covenant is the same.
Now there are many, many instances of the covenant in the Bible, and at this point the dispensationalists get into any number of covenants you see. There is the covenant at creation, there is the covenant with Noah, there is the covenant with Abraham, the covenant Moses, and other instances of the renewal of the covenant, before and after. So that you can wind up as some people do with umpteen covenants, and therefore if you regard each covenant as a totally new covenant you end up with umpteen dispensations.
But when you see them as different only in that it is a different person or a different group, but one and the same God making one and the same covenant with people, then you have to say that there is one covenant throughout Scripture; therefore one plan of salvation throughout Scripture, by grace.
Salvation is always an act of law and an act of grace. It is an act of law because it requires at all times atonement - God provides that atonement, in the Old Testament symbolically and typically in the animal sacrifices, which typified Christ- in the New Testament Christ, as the atonement, the sacrifice for sin. That necessity is because the penalty for sin is death, the law of God requires it, and the law of God must be satisfied; there can be no salvation apart from the satisfaction of the law. So salvation is an act of law within the Trinity; the Son satisfying the legal requirements of the Trinity. But it is an act of grace towards us, in that the satisfaction rendered by the second person of the Trinity in His incarnation is applied to us, and our sin is cancelled. So it is an act of grace.
Now that is exactly what the sacrificial system of the Old Testament set forth. It is exactly what the sacrifice of our Lord openly sets forth. It is one and the same plan of salvation, one and the same covenant, but with different peoples. We must remember that fact because it is important for us to understand the events of our time. Because in origin almost every modern state in Western Europe and the Americas began in some sense as a covenant people. We as the United States began as a covenant people; we saw ourselves as such. The very fact that the oath of office was taken on Deuteronomy 28 tells us that they saw themselves as a covenant people.
The fact that we have broken the covenant only brings judgement upon us unless we return to it. But it does not mean that if tomorrow God singles out a new group of nations in Africa or Asia to be His covenant peoples that it is a new covenant, and a new plan of salvation.