Both the Jews and the Arabs claim that they are descendants of Abraham. Abraham had two sons, Isaac and Ishmael. The Jews claim that they are descendants of Isaac, and the Arabs claim that they are descendants of Ishmael.
Isaac was the true heir of Abraham because his mother was Abraham’s wife, Sarah. Ishmael’s mother was Sarah’s Egyptian slave, Hagar. By the customs of that time, Abraham was allowed to have a son through his wife’s slave if the wife could not bear children. God, however, gave Abraham a son through his wife Sarah when they were very old.
God promised to Abraham and Sarah that He would establish His covenant (i.e. contract) with Isaac and not with Ishmael. Ishmael would be given certain temporal blessings, but God’s eternal and spiritual blessings would go to Isaac and his descendants. These blessings would be given through a seed (i.e. descendant) of Isaac, namely Jesus Christ.
The Bible clearly explains that all who believe in Jesus Christ are the spiritual descendants of Isaac. They have had a change in their nature which is described as a new birth. They are children of promise. They are free, and not under bondage. They are the true children of Abraham and heirs of the blessings God had promised to him.
On the other hand, those who trust in the keeping of the law, i.e. in their good deeds, for acceptance with God are the descendants of Ishmael, regardless of their ethnic background. Like Ishmael, they are children born in the natural way. They have not experienced the new birth brought about by the Holy Spirit. They are slaves to their sinful nature. They are not accepted as citizens of heaven.