If it were only lawkeepers who were heirs of the promises, Paul argues, then faith would be made void, or useless.  Thus, the promises of God would become of no effect; for did not Abraham himself enter into the fullness of the promises of God by faith, rather than by works?  If Abraham obtained his benefits by faith, while we must strive for them by works, then we are doomed to much harder conditions than was the great patriarch.  But this can never be the case.  Salvation is not upon different terms for one man than for others.  Abraham, and every person before or after him, can only be saved one way: by believing the promises of God, as they relate to and are fulfilled in the person and work of His Son, Jesus Christ.

In fact, Paul goes on to argue, it was impossible that men should obtain the benefit the promises by the law, because the law could produce nothing for men but wrath.  We need not analyze that argument again, because the apostle has painstakingly proved that very thing in the first three chapters.  I need only quote his summary words in 3:20, “Therefore by the deeds of the law there shall no flesh be justified in His sight: for by the law is the knowledge of sin.”  Since the law can never justify us, it can only condemn us.  It can never be neutral towards us.  Since we are sinners, and it is righteous, it justly condemns us.  Therefore, we can never become heirs of God’s glorious promises by obedience to that very instrument which has already pronounced condemnation upon us.  And, Paul adds, if there were no law, there should be no transgression; for there can be no wrongdoing if there is no standard of right and wrong to judge actions by.  In that case, there would be no need for Gospel promises in the first place.  But since there is a law, and since it can only convince us as transgressors, we must look for hope from some other source than that law.  Only, then, in a Gospel based upon faith, is there ground for such promises as were made to Abraham and to his seed.  Paul would cut out from under our feet any hope that we may have of becoming heirs of God by the works of the law, and drive us to the conclusion that we can only enter into the blessings of the kingdom of God through faith in Jesus Christ.