21 Tell me, you who desire to be under the law, do you not listen to the law?22 For it is written that Abraham had two sons, 23 But 24 Now this may be interpreted allegorically: these women are two 25 Now Hagar is Mount Sinai in Arabia; she corresponds to the present Jerusalem, for she is in slavery with her children. 26 But 27 For it is written,
break forth and cry aloud, you who are not in labor!
For the children of the desolate one will be more
than those of the one who has a husband.”
28 Now you, brothers, 29 But just as at that time he who was born according to the flesh 30 But what does the Scripture say? 31 So, brothers, we are not children of the slave but In what sense was Ishmael (the child born through Hagar) born in the ordinary way? The answer lies not so much in the physicality of the conception, but rather in the fact that he was conceived through human scheming and planning — the way of the flesh: the way of works and self-effort. In contrast, Isaac was born by the free woman, Sarah. His conception was supernatural because the Holy Spirit had miraculously enabled Abraham and Sarah to conceive a child after she was far beyond the age of childbearing. When Isaac was born, his father was 100 and his mother 90 (Genesis 17:27; 21:5).
The conception of Ishmael may be considered analogous to the way of religious self-effort and works-based righteousness. The conception of Isaac is analogous to the way of trust in the promises of God, and God’s imputed righteousness. While Ishmael typifies those who have been born naturally (that is, those who place their trust in their own works and merits), Isaac typifies those who have had been born of the spirit through trusting in the promises of God and in the completed work of the Lord Jesus Christ.
Paul then tells us that the two women (Sarah and Hagar) represent two covenants. Hagar represents the covenant of law and works, while Sarah represents the covenant of grace and faith.
The Old Covenant of law was given at Mount Sinai to Moses. Because the terms of the covenant were not possible for us to abide by perfectly, it produced slaves, chained to their master of the law from whom they would never be able to escape. The descendants of Hagar (through Ishmael) eventually moved into the desert areas to the east and south of the Promised Land, and eventually came to be known as the Arabs and their territory as Arabia. It is rather significant that Mount Sinai (representing the law) is located on what is known today as the Arabian Peninsula.
Paul notes that Hagar and Mount Sinai correspond to the present city of Jerusalem. He speaks of the first Jerusalem as present, suggesting that he is here talking about the actual city of Jerusalem. In the same way God chose Mount Sinai to be the geographical location in which he would deliver the Old Covenant to Moses, so he also chose Jerusalem as the geographical location in which to the Old Covenant would be propagated and exemplified. In this type, both locations are intended to represent the Old Covenant of law and works and the bondage and slavery that they produce.
The city of Jerusalem is also the city in which the New Covenant is established in the death and resurrection of Christ. But the New Covenant of grace was rejected by the Jews, and so — much like Mount Sinai in Arabia — Hagar still figuratively dwells in slavery with her children. In Paul’s day, most of Jerusalem’s inhabitants were in deep bondage and slavery to damning legalism, ritual, ceremony and self-effort.
Conversely, the spiritual descendants of Sarah (through Isaac) live in the Jerusalem above and are free, because she is our mother. The inhabitants of this heavenly Jerusalem are free from the slavery that comes from legalism and works-based self-righteousness. As Jesus said in John 8:36, “If therefore the Son shall make you free, you shall be free indeed.”
Paul continues, by quoting from Isaiah 54: “Be glad, barren woman, you who never bore a child; shout for joy and cry aloud, you who were never in labour; because more are the children of the desolate woman than of her who has a husband.”
Paul’s point here is that just as freedom came once again to the nation of Israel in Babylonian captivity, so it would come to the people in captivity to the law.
Paul also discusses the result of being a spiritual descendant of Isaac. Just as in that time, when there was resentment of Isaac by Ishmael, those who are spiritual descendants of Isaac are still persecuted by the spiritual descendants of Ishmael. Indeed, when Abraham held a feast to celebrate Isaac’s weaning, Ishmael mocked the occasion. And so it is now also. Those who hold to salvation by works hate those who proclaim salvation by grace alone without works.
Paul concludes by noting that just as the Scripture says “Get rid of the slave woman and her son, for the slave woman’s son will never share in the inheritance with the free woman’s son,” so the persecutors and slaves of the law will be thrown out of Abraham’s spiritual household.
Paul further remarks that “It is for freedom that Christ has set us free. Stand firm, then, and do not let yourselves be burdened again by a yoke of slavery.” In other words, Paul is asking, “Why on earth would anyone want to go back to being a slave like Ishmael, in view of the freedom made available in Christ?”
The question thus arises, is all this tightly interwoven symbolism explicable as the result of happy happenstance? Or is it too much to be attributed to blind coincidence? I don’t think these deep theological meanings are being imposed on the text, nor do I think the text is stretched or strained by Paul’s analysis. It is also significant that, while Isaac was the ancestor of Jesus Christ himself (who opened the way of salvation through grace, thus freeing us from obligation to the law), Ishmael was the ancestor of the Islamic prophet Muhammad. Muhammad was of Arabian descent, and the Islamic religion is based around Arabia (where Mount Sinai is to be found), and based on a legalistic system of salvation through one’s meritorious deeds and works, and keeping the Law. This brings forth slavery, whereas Isaac’s descendent, Jesus Christ, brings forth freedom through trusting the promises of God and in the merit of His completed work alone.
Note also that Isaac is the one ultimately laid on the alter in Genesis 22, and spared by the slaughter of a substitute, in the form of a ram caught by its horns in the bush. Note that the supplication of the ram implies that the ultimate Lamb of God (as had been promised on the way up Mount Moriah: “God will provide Himself the Lamb for the burnt offering”) was still to be provided, hence Abraham names the mountain “The Lord Will Provide”, saying “On the Mountain of the Lord, It Shall Be Provided” (note the future tense). Isaac carried the wood for his own sacrifice up the mountain, in a fashion similar to the manner in which Jesus carried his own cross for his ultimate sacrifice for sins. And The mountain on which these events unfolded is also thought to be the mountain on which our Lord was crucified.
When one considers this foreshadow of the gospel, in conjunction with the other mass of cumulative evidence from multi-disciplinary sources, I think one has very strong reason to think that the Christian worldview does indeed add up. Such intricate weaving of gospel threads throughout the fabric of the Old Testament is something which only God could do.
Source: http://www.answeringmuslims.com/2015/12/ishmael-and-isaac-muhammad-and-jesus.html