Abraham moved from Mamre southward to Gerar to make his home. Soon afterwards, Isaac, the promised child was born when Abraham was one hundred and Sarah was ninety years of age.
When the time came for Isaac to be weaned (at 2 to 3 years of age), Abraham made a great feast, which was customary at that time. Ishmael, who was 14 or 15 years old, began scoffing. Nothing was recorded about what he did or said, but Sarah was most upset. She demanded that Abraham cast “this bondwoman (Hagar) and her son” out of the family; “for the son of this bondwoman shall not be heir with my son, namely with Isaac.” (Paul used this incident as an allegory in his letter to the Galatian church to illustrate the inferiority of the Law of Moses to the New Testament law of Christ. See Gal. 4:21-31.)
Casting out Hagar and her son was difficult for Abraham, for Ishmael was his first-born son. God, however, in His providence instructed him to follow Sarah’s wishes, “for in Isaac your seed shall be called. Yet I will also make a nation of the son of the bondwoman, because he is your seed.”
As they wandered in the Wilderness of Beersheba, their food and water being depleted, Hagar and Ishmael prepared to die. God, as He had promised Abraham intervened and they survived. Hagar, an Egyptian native found a wife for Ishmael in the land of Egypt.
After several years, God called Abraham for a test of his faith. He instructed him to take Isaac, his only son (heir) and offer him as a burnt offering.
Without faith, Abraham could have reasoned that God had promised him that great things would be done through Isaac. If he were to offer him as a burnt sacrifice, this could not happen and therefore, refused to obey the command of God.
Abraham’s statements, “The lad and I will go yonder and worship, and we will come back to you” and “My son, God will provide for Himself the lamb for a burnt offering” show the deep faith that he had in God and His promises. He believed that God would raise Isaac from the dead, which He did in a figurative sense.