This commentary was previously inadvertently posted out of sync with the Bible narrative, I removed, corrected and rewrote it as there is much to be drawn from this event.
The Lord visited Sarah as he had said, and the Lord did to Sarah as he had promised. And Sarah conceived, and bore Abraham a son in his old age at the time of which God had spoken to him. Abraham called the name of his son who was born to him, whom Sarah bore him, Isaac. And Abraham circumcised his son Isaac when he was eight days old, as God had commanded him. Abraham was a hundred years old when his son Isaac was born to him. And Sarah said, “God has made laughter for me; every one who hears will laugh over me.” And she said, “Who would have said to Abraham that Sarah would suckle children? Yet I have borne him a son in his old age.”
And the child grew, and was weaned; and Abraham made a great feast on the day that Isaac was weaned. But Sarah saw the son of Hagar the Egyptian, whom she had borne to Abraham, playing with her son Isaac. So she said to Abraham, “Cast out this slave woman with her son; for the son of this slave woman shall not be heir with my son Isaac.” And the thing was very displeasing to Abraham on account of his son. But God said to Abraham, “Be not displeased because of the lad and because of your slave woman; whatever Sarah says to you, do as she tells you, for through Isaac shall your descendants be named. And I will make a nation of the son of the slave woman also, because he is your offspring.” So Abraham rose early in the morning, and took bread and a skin of water, and gave it to Hagar, putting it on her shoulder, along with the child, and sent her away. And she departed, and wandered in the wilderness of Beer-sheba. (Genesis 21: 1-14)
It may seem that Sarah was acting harshly however Abraham showed a kind heart and loyalty toward Hagar and Ishmael, there was something more at play though. Sarah knew early in life that she was barren and that Abraham wanted an heir, and although God had made it plain that Abraham would father a son through Sarah, they both showed distrust in God’s word and she gave her slave woman to Abraham, and Ishmael was born from that union. That event was devoid of faith in God’s promise and was in essence a carnal act of disobedience, not one not of faith but of the flesh as they acted on their own accord outside of the will of God. In today’s world Ishmael would be considered the bastard son and hardly fit to be the heir of God’s promise. As a result the descendants of Ishmael would be forever filled with animosity and murderous envy towards the descendants of Isaac which is in essence a repeat of Cain’s envious murder of his own brother Abel.
Centuries later the Apostle Paul would use it as an example to instruct the first Jewish Christians who were confused about the law and whether or not they were still required to remain under and observe Jewish law, when Christ himself had paid the penalty for all mankind who have failed under the law.
“Tell me, you who desire to be under law, do you not hear the law? For it is written that Abraham had two sons, one by a slave and one by a free woman. But the son of the slave was born according to the flesh, the son of the free woman through promise. Now this is an allegory: these women are two covenants. One is from Mount Sinai, bearing children for slavery; she is Hagar. Now Hagar is Mount Sinai in Arabia; she corresponds to the present Jerusalem, for she is in slavery with her children. But the Jerusalem above is free, and she is our mother. For it is written,
‘Rejoice, O barren one who does not bear; break forth and shout, you who are not in travail; for the children of the desolate one are many more than the children of her that is married.’ Now we, brethren, like Isaac, are children of promise. But as at that time he who was born according to the flesh persecuted him who was born according to the Spirit, so it is now. But what does the scripture say? ‘Cast out the slave and her son; for the son of the slave shall not inherit with the son of the free woman.’ So, brethren, we are not children of the slave but of the free woman. For freedom Christ has set us free; stand fast therefore, and do not submit again to a yoke of slavery.”(Galatians 4:21-5:1)
Paul referring to Mount Sinai is pointing out how God gave Moses the law that no man can follow perfectly, which is the requirement for acceptance by God. Failure under the law resulted in sin and the requirement for sin is death and eternal separation from God. He likened it to Jerusalem and living under the Law. “since all have sinned and fall short of the glory of God.” (Romans 3:23)
It is written: “For whoever keeps the whole law and yet stumbles in one point, he has become guilty of all.” (James 2:10)
There is no one on earth that has ever kept the Ten Commandments perfectly let alone the infinite number of associated laws that were tacked on for the Jews by their Jewish legislators of old. In modern day society we have a vast number if civil laws that spring in essence from those original commandments and we routinely fail under them as well.
Paul goes on and refers to Sarah, a free woman whose son was heir of the promise and through whom Christ the Messiah would come and pay the penalty for the broken laws of all of mankind. He points out that we as believers have positionally cast out the slave, that is our former state, and accepted the freedom provided through Christ. We are to stand fast and not submit again to a yoke of slavery which is sin under the law.
“But the Jerusalem above is free, and she is our mother.” Here Paul is referring to the union of believers we know as the church, and makes a distinction between the believers and unbelievers implying that the church is the bride of Christ. “For it is written,‘Rejoice, O barren one who does not bear; break forth and shout, you who are not in travail; for the children of the desolate one are many more than the children of her that is married.’ Now we, brethren, like Isaac, are children of promise.”