God made a covenant with Abraham, and it was His promise that he would become the father of many nations. Throughout all generations this promise has been kept not by the law, but was ordained through Christ by faith to His people. (Galatians 3:16-22). Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ.And this I say, that the covenant, that was confirmed before of God in Christ, the law, which was four hundred and thirty years after, cannot disannul, that it should make the promise of none effect. For if the inheritance be of the law, it is no more of promise: but God gave it to Abraham by promise. Wherefore then serveth the law? It was added because of transgressions, till the seed should come to whom the promise was made; and it was ordained by angels in the hand of a mediator. Now a mediator is not a mediator of one, but God is one. Is the law then against the promises of God? God forbid: for if there had been a law given which could have given life, verily righteousness should have been by the law. But the scripture hath concluded all under sin, that the promise by faith of Jesus Christ might be given to them that believe.
Abraham obtained the promise from God after he did not withhold his son Isaac as a sacrifice and by such faith was a ram caught in a thicket made available instead for the sacrifice. By this action his seed would multiply as the stars of heaven. (Genesis 22:13-18) And Abraham lifted up his eyes, and looked, and behold behind him a ram caught in a thicket by his horns: and Abraham went and took the ram, and offered him up for a burnt offering in the stead of his son. And Abraham called the name of that place Jehovahjireh: as it is said to this day, In the mount of the Lord it shall be seen.And the angel of the Lord called unto Abraham out of heaven the second time,And said, By myself have I sworn, saith the Lord, for because thou hast done this thing, and hast not withheld thy son, thine only son: That in blessing I will bless thee, and in multiplying I will multiply thy seed as the stars of the heaven, and as the sand which is upon the sea shore; and thy seed shall possess the gate of his enemies;And in thy seed shall all the nations of the earth be blessed; because thou hast obeyed my voice…… (Hebrews 6:10-15).
We as Christians have become heirs according to the promise given to Abraham by being baptized in Christ! (Galatians 3:25-29). But after that faith is come, we are no longer under a schoolmaster. For ye are all the children of God by faith in Christ Jesus. For as many of you as have been baptized into Christ have put on Christ.There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus.And if ye be Christ’s, then are ye Abraham’s seed, and heirs according to the promise.