Romans 4:13-17

Romans 4:13-17 It was not through the law that Abraham and his offspring received the promise that he would be heir of the world, but through the righteousness that comes by faith. For if those who depend on the law are heirs, faith means nothing and the promise is worthless, because the law brings wrath. And where there is no law there is no transgression.
Therefore, the promise comes by faith, so that it may be by grace and may be guaranteed to all Abraham’s offspring—not only to those who are of the law but also to those who have the faith of Abraham. He is the father of us all. As it is written: “I have made you a father of many nations.”  He is our father in the sight of God, in whom he believed—the God who gives life to the dead and calls into being things that were not.

It is through the righteousness that comes by faith that enables Abraham and his offspring to receive the promise… not the Law of Moses.  If it is the natural descendents of Abraham who are the heirs, then faith means nothing and the promise is worthless because the law brings only wrath.  The law of Moses has no power to save and cannot save.  Anyone who is depending on their own law keeping or works to be save is depending on fools gold. 

Therefore, the promise comes by grace alone through faith alone in Christ alone.  This promise is only for those who have a personal faith in Christ.  As the Apostle John said in John 1:12-13… It does not depend on children of natural descent, nor of human decision or a husband’s will, but only those born of God.  While circumcising Old Covenant Jews placed them in a physical covenant with God, it did not place them in a spiritual covenant.  Likewise, baptizing infants does not place them in a spiritual covenant.  In fact it does not place them in any covenant since the Mosaic Covenant has ended [Heb. 8:13, 2 Cor. 3, Gal. 3, etc.].