The only way there is to be saved, by trusting in the work of Christ alone. Because God is just, sin must be punished. Because we are sinners, that is bad news for us. The promise of God to Adam and Eve, however, was that the Seed of the Woman would have His heel bruised, while He crushes the head of the serpent. God took the man-made coverings our first parents fashioned and gave them animal skins to cover them, foreshadowing the need for the shedding of blood by a substitute.
These shadows continued throughout the Old Testament. With each passing generation, however, the shadows of the promise began to recede. The gospel, in its most nascent form, was given in Genesis 3, but it grew in clarity. Abraham’s sacrifice of Isaac, Joseph’s multiple deaths, burials, “resurrections,” Moses striking the rock in the wilderness, all these pointed to the coming of a substitute. The sacrificial system God gave His people made the promise still more clear.
We are all, however, given to confusing the sign with the thing signified. Adam and Eve were not redeemed by the animals whose skins they wore. And not a soul was saved by the sacrifice of bulls and goats. Were such sufficient, Christ would not have ever needed to come. Instead they pointed forward to the future hope, the future hope that secured redemption for those who believed. The redeemed in the Old Testament were redeemed by the work of Christ that was to come, which they appropriated by faith. As we look backward to His finished work for us, and rest in it, so they looked forward to His coming work for them, and rested in it.
For Adam and Eve the object of their faith was that first simple promise. I doubt they had a deep understanding of what the promise meant, but I believe they believed it was their only hope. For the earlier generations in the Promised Land the object of their faith included a better understanding of what the sacrificial system meant, and they believed it was their only hope. With the prophet Isaiah the meaning of the promise became more clear still, as he described for God’s people the suffering servant who would be bruised for our healing.
There is but one people of God, those who are covered by the blood of Christ. There is but one way to peace with God, resting in the work of Christ. There is but one gospel, the promise of God that He has reconciled us to Himself in pouring out His wrath for us upon Him. As they looked forward through the sacrifices, so we look backward through the table of the Lord. To rest in either would be deadly. To rest in the one each represents is to be at peace with the living God, to be adopted into His family, to eat as His children at His table. There are not two ways into the kingdom, just one.