Scripture gives us the goal of this covenant:
Gen. 18:19 For I have chosen him, that he may command his children and his household after him to keep the way of the LORD by doing righteousness and justice, so that the LORD may bring to Abraham what he has promised him.”
This Scripture not only declares that the Lord chose Abraham for a reason (that reason was not in Abraham himself), but it also tells us that there is a certain conditionality involved in this covenant relationship. As we noted above concerning Genesis 17:6-8 about God’s sovereignty and will in the matter of the covenant and the promises, so we noted the conditionality of the fulfillment of these promises upon Abraham’s and his posterity’s obedience to the Lord’s command (Gen. 17:9-14). So here also we meet the same thing. God has chosen Abraham for the purpose that Abraham may teach his posterity about the way of God in doing what is good and righteous before the sight of God so that the Lord will bring His promises to pass. What if Israel remained hardhearted and disobedient? Will God honor those who despise Him (1 Sam 2:30)? Certainly not and we know of the many judgments that fell upon Israel for their disobedience. But the inheritance of the promises is dependent upon them doing that which is righteous and just before God according to His way. The same idea is also given to the child of the promise, Isaac –
Gen. 26:4-5 I will multiply your offspring as the stars of heaven and will give to your offspring all these lands. And in your offspring all the nations of the earth shall be blessed, 5 because Abraham obeyed my voice and kept my charge, my commandments, my statutes, and my laws.”
God will fulfill the promise because there was a condition met. This is not an unconditional covenant like the Covenant of Grace. Among other things, we see that the Abrahamic Covenant cannot be an administration of the Covenant of Grace, although it is gracious, as all the Lord’s covenants are. Even the covenant with Adam has grace in it as God is under no obligation to enter into a relationship with man and promise him great blessings. Yet this cannot properly be called an administration of the Covenant of Grace, at least not in 1689 Federalism. Furthermore, it is a breakable covenant and it administers curses to covenant breakers (Gen. 17:14), which the New Covenant is not and does not. All those belonging to Abraham who are not circumcised, have broken this covenant and fall under its curse, i.e., they are cut off from the covena...