Abraham had two sons, Ishmael and Isaac.
Ishmael was born after the flesh (by human effort) and Isaac was born according to the promise. Ishmael was a descendant of Abraham as was Isaac, but Isaac was the child of promise.
Isaac had two sons, Esau and Jacob.
Esau was the heir to the blessing (the promise God made to Abraham) because he was Isaac’s first born son. However, Esau did not esteem the blessing and sold his birth right. Jacob esteemed the birth right and desired the blessing. Through a series of events Jacob inherited the blessing.
Esau was a descendant of Abraham as was Jacob, but God loved Jacob and hated Esau because Jacob desired the blessing and Esau despised it.
As it was with Ishmael and Isaac, and Esau and Jacob, so it was with the nation of Israel. Within Israel, there were those who were Abraham’s descendants according to the flesh, but they were not heirs according to the promise, they were not the true children of Abraham.
In John 8 Jesus was opposed by some religious Jews who boasted that they were the children of Abraham. In John 8:36 -39 we read the following:
If the Son therefore shall make you free, ye shall be free indeed. I know that ye are Abraham’s seed; but ye seek to kill me, because my word hath no place in you. I speak that which I have seen with my Father: and ye do that which ye have seen with your father. They answered and said unto him, Abraham is our father. Jesus saith unto them, If ye were Abraham’s children, ye would do the works of Abraham.
Jesus goes on to tell them that not only were they not Abraham’s children but they were actually the children of the devil even though they were physical descendants of Abraham.
In Romans 9:7-8, the apostle Paul tells us the following:
Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called. That is, they which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed.
We can see from these words of Paul that not all in Israel were the children of the promise, and therefore were not considered “the seed of Abraham” in the eyes of God. This is consistent with the words of Jesus in John 8 mentioned above.
Only those who were children of the promise were counted as the seed. Who then are the children of promise? They are those who are the children of Abraham “by faith” and who “by faith” walk in the steps of Abraham’s faith.
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. For IF THEY which are of the law (national Israel) be heirs, faith is made void, and THE PROMISE made of none effect: Because the law worketh wrath: for where no law is, there is no transgression. 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, (As it is written, I have made thee a father OF MANY NATIONS,) before him whom he believed, even God, who quickeneth the dead, and calleth those things which be not as though they were (Romans 4:13-17).
The promise which God made to Abraham was that he would be the father of “many nations.” Abraham believed this promise and Abraham was declared righteous in the sight of God.
According to Galatians 3:8, when God made this promise to Abraham, He preached or declared the gospel to him. In the fullest sense of the word, Abraham believed the gospel when he believed God’s promise to make him the father of many nations and was declare righteous!
Christ is the promised seed of Abraham (Galatians 3:16) through whom the blessing promised to Abraham comes to fruition, for it is only in and through Jesus Christ that a person can be justified in the sight of God. Abraham was justified by God because he believed the promise God made “in Christ” (Galatians 3:17) when God promised to make Him the father of many nations through Christ the promised seed of the covenant.
Being an heir to the promise God made to Abraham comes only through faith in Jesus. This does not apply to Gentiles alone, but to Jews and Gentiles alike. Being a descendant of Abraham “after the flesh” is not the same as being “an heir to the promise.”
As we have seen, there are those who are Abraham’s seed ACCORDING TO THE FLESH, and there are those who are Abraham’s seed ACCORDING TO THE PROMISE. Only those who are Abraham’s seed according to the promise are the children of God!
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 (Galatians 3:26-29).