13 For the promise, that he should be the heir of the world, was not to Abraham, or to his seed, through the law, but through the righteousness of faith. 14 For if they which are of the law be heirs, faith is made void, and the promise made of none effect: 15 Because the law worketh wrath: for where no law is, there is no transgression. 16 Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all, (Romans 4:13-16 KJV)
Abraham, father of the faithful
It was also before the giving of the law (Ro 4:13-16). The promise was made to Abraham long before the law (Ga 3:17-18). The promise was that he should be heir of the world—whether of Canaan, or of many nations, or of the blessings of life, but chiefly of Christ, the seed (Ga 3:16), in whom all nations are blessed (Ge 12:3).
This promise was not through the law, but through the righteousness of faith, upon that believing which was counted to him for righteousness, when he trusted God in leaving his country (Heb 11:8). If inheritance were by the law, then faith would be void; for if perfect obedience were required, the promise could never take effect. The law worketh wrath (Ro 4:14-15). Where there is law, there is transgression, and so wrath; therefore the inheritance cannot be by the law.
The promise was made by faith for three reasons (Ro 4:16). First, that it might be by grace, so that grace would have all the honour (Eph 2:8; Ps 115:1). Second, that it might be sure, for the covenant of works failed through man’s weakness; but faith rests on Christ, the trustee of salvation (2Sa 23:5). Third, that it might be sure to all the seed, both Jew and Gentile (Ro 9:4). Therefore God contrived it by faith, that it might extend to all believers. As it is written (Ge 17:5; Ro 4:17), “A father of many nations have I made thee.”