There are two prominent features in this chapter of which the Christian should take note. The first is the birth of the son (Isaac) that God promised to Abraham (then under the name of Abram) in chapter 15 and verse 4 that would establish Abraham’s descendants through whom God would fulfill His covenant promises to Abraham as recorded in chapter 12 and verses 2 and 3 (repeated in chapters 15 and 17), the most significant aspect of which would be the birth of Jesus Christ. Significantly, the birth of Isaac bares a strong resemblance to and thereby foreshadows the birth of Christ approximately 1,900 years later—to be discussed in the body of this commentary.

The second prominent feature is the relationship between Abraham’s oldest son Ishmael, who was birthed by Hagar the servant, and Abraham’s youngest son Isaac, who was birthed by Abraham’s wife Sarah; a relationship that has particular interest to and application for the Christian today in light of apostle Paul’s teachings of the antagonisms between the flesh and the Spirit and between the bondage of the law and the freedom of grace (faith) as depicted in Galatians 4 and Romans 4—to be discussed in the body of this commentary. These are cardinal truths, which mark the difference between “religion” (the approbation of God’s through self-merit) and Christianity (a union or relationship with a Person, Jesus Christ) and which are foundation stones in the argument that once a Christian is saved there can be no going back to a lost condition.

Of secondary importance but not to be taken lightly, specifically in light of present world on-going conflicts between the descendants of Isaac (Israelites) and Ishmael (Palestinians), is God’s treatment of Hagar and her son Ishmael. Finally, there is the covenant between Abraham and Abimelech at Beer-sheba.

There are several important truths contained in these verses, not the least of which is that God carries out His purpose and plan in accordance with His Word always in a meticulous fashion and in accordance with His prescribed timetable, as seen in the birth of Isaac as He had said and at the set time of which God had spoken to Abraham. The name Isaac, which was given by God for the boy in Genesis 17:19, signifies “he laughs” or “he who laughs” (and indication of the joy this son brought to both Abraham and Sarah, and, ultimately to the world). Isaac was born most likely in Gerar to Abraham and Sarah when they were 100 and 90 years old respectively. He was the first of Abraham’s household to be circumcised in the normal course, when eight days old (verse 4). Other than these few verses in this chapter, nothing is known of the early boyhood of Isaac. He is next seen in the next chapter as a young man who is big and strong enough to carry the wood for the altar fire up the mountain slope. He was 37 years old when his mother died in Hebron, was married to Rebekah when he was 40 years old, was 60 years old when his twin offspring of Esau and Jacob were born, and was 75 years old when his father died at the age of 175, a time when he and his brother Ishmael came together probably for the last time in their lives.

Isaac was a “child of faith,” not only a product of Abraham’s faith in God and His Word but also of Sarah’s faith (Hebrews 11:11), which emerged subsequent to her first reaction of incredulous laughter at the hearing of the prediction that she would give birth; and which faith became apparent in Isaac at an early age. It was faith that gave Abraham a “standing in righteousness” before God. Isaac was the fruit of justifying faith (Romans 4:18-22). This faith was borne out in Abraham’s firm belief in God and His Word of the promised natural son by his wife Sarah even when he knew of the inability (“deadness”—Romans 4:19; Hebrews 11:12) of he and Sarah at their age to bear children. It was further borne out in his obedience to God in offering Isaac as a sacrifice. Abraham, through faith, knew that God would keep His covenant promises, of which Isaac was a key part, and he also firmly believed that if God allowed Isaac to die on the sacrificial altar, God would raise him back to life; therefore, Isaac became a figure (symbol) of “life from the dead” (the “new life in Christ”) and the resurrection (Hebrews 11:17-19; Romans 6:3-5). Most importantly, Isaac prefigures Jesus Christ, as the obedient son, who “became obedient to the point of death, even the death of the cross.” (Philippians 2:8)

In fact, Isaac prefigured Jesus Christ in several ways; notice the following comparisons of the two:

Once Isaac was weaned from his mother’s milk, Abraham threw a great feast in celebration.

Genesis 21:9-13

From a human viewpoint it is understandable that Abraham was troubled over what must have appeared to him to be an overreaction by Sarah to Ishmael’s scoffing (Hebrew: tsachaq, to mock or laugh outright with scorn) on the day that Abraham celebrated Isaac being weaned from Sarah, a recognition of his maturing to the next higher stage. After all, Ishmael was also Abraham’s son, his firstborn at that. Scripture does not indicate that Ishmael was mocking Isaac, Abraham or the celebration; it only states that Sarah noticed his attitude, which apparently produced a well-matched outward expression, and was greatly displeased with it. Ishmael’s attitude and reaction does appear to indicate that he had no love or respect for his younger half-brother.

As a result of her deep displeasure, Sarah instructed Abraham to kick Hagar and Ishmael out of the household, because she would not tolerate Ishmael being Abraham’s heir along with Isaac. And although this greatly depressed Abraham, God comforted him by (1) allowing him to know that Sarah’s instruction was appropriate in that it was through Isaac that God’s covenant with Abraham would be administered—that Abraham’s “seed shall be called,” a forecast of the Seed Jesus Christ who would become a blessing to all nations and by means of the cross (His vicarious and sacrificial death upon it) crush the head of Satan; and (2) informing him that he need not worry about Hagar’s and Ishmael’s future, for God would also make a great nation of Ishmael.

But the real significance of the relationship between Sarah and Hagar and their sons is actually found in the apostle Paul’s teachings in the New Testament. In Galatians 4 and Romans 4 the apostle utilizes the real-life opposing relationship between Sarah and her son Isaac and Hagar and her son Ishmael to portray two very important biblical doctrines, as follow:

The Bible student would do well to closely examine the chapters of Galatians 4 and Romans 4 in connection with this passage in Genesis 21. The truths found therein will expel any perceived connection between Christianity and “religion.” As used here and throughout this commentator’s writings, “religion” is man’s efforts to achieve the approbation (approval) of God. Or to put it another way, it is the belief that the way to heaven is through good deeds or works. On the other hand, Christianity is a union (relationship) with the person of Jesus Christ that only may be apprehended with genuine (non-meritorious) faith. The union with Christ, once obtained by placing one’s full and genuine confidence (trust, faith) in Him for one’s personal salvation, is both absolute and eternally permanent—never to be retracted by any means on the part of man or God.

And herein is the contrast and never-ending struggle that has existed from the earliest of time at the fall of man in the Garden of Eden, as portrayed by the apostle Paul in the symbolic conflict between the bondswoman Hagar and her son Ishmael born as a result of Abraham’s scheming intervention and the freewoman Sarah and her son Isaac born miraculously by the hand of God and in accordance with His unilateral covenant with Abraham:

The name “Ishmael” in Hebrew means “God hears” and is related to the experience wherein God heard the anguished prayer of Hagar in her flight from the household of Abraham in Genesis 16:11 and where He hears the voice of Ishmael in this passage. Here God confirms to Hagar what He has already told Abraham about Ishmael’s survival and proliferation as a great nation. Then God provides sustaining water for their journey.

As imperfect a child of God as was Abraham, God continued to support him. Because of this Abimelech granted Abraham maximum respect and looked to him for a blessing for him, his household and his descendants. But during Abimelech’s appeal to Abraham for this, Abraham interjected a complaint to Abimelech, that Abimelech’s servants had stolen his water well. This brought immediate rectifying action on the part of Abimelech. Both men immediately made a covenant establishing an agreement between the two that Abraham would not deal falsely with Abimelech, his household or his descendants; but would deal in kindness toward him. Probably as a subsection of the covenant between them, the ownership of the well was “deeded over” to Abraham. And Abraham sealed the agreement with a presentation of certain sheep and oxen; in addition he gave Abimelech “seven ewe lambs.” Upon the completion of the covenant between Abimelech and Abraham, Abraham named the place where they had made the covenant Beersheba.

Regardless of Abraham’s faults, he was consistent in “calling on the name of the Lord,” which is an expression that conveys that Abraham placed his faith in and depended on the Lord, even though as most children of God, he failed Him repeated.