Abraham actually had more sons through Keturah, but for the purposes of Paul's allegory, he focuses on Ishmael, the son through Hagar, and Isaac, the son of promise through Sarah.
Given that the false teachers were trying to convince the Galatians to turn to a Gnostic form of Judaism, Abraham would have been a character who would have been highly respected in their eyes (the Jews in Jesus' time trusted in descent from Abraham for salvation). Paul uses the example of Abraham throughout this epistle because he (Abraham) simultaneously served as someone that they would have looked up to, as well as a testament that they (the Galatians) were approaching this the wrong way—different from the way Abraham did.
Physical descent does not matter as far as the spiritual promises are concerned; Christ castigated the Jews for thinking that they could rely on being physical descendants of Abraham as a means of gaining favor with God. Christ showed that where it really counted was in behaving like Abraham—which the Jews did not.
Paul, in an attempt to help the Galatians to understand the covenants, is likening the Old Covenant to being born to a "bondmaid" (a female slave or servant) while the New Covenant is compared to being born of a "freewoman" (someone who is a citizen; unrestrained; not a slave; exempt from liability; at liberty). The carnal mind, as described by Romans 8:7, leaps to the conclusion that the New Covenant gives freedom from the confines of law, while the Old Covenant keeps one in bondage to a set of archaic rules. Nothing could be further from the truth.
The apostle James twice refers to the law as the "law of liberty" (James 1:25; 2:12). He could do this because when God was giving the Ten Commandments to Israel, He prefaced them with the declaration, "I am the LORD your God, who brought you out of the land of Egypt, out of the house of bondage" (Exodus 20:2). This—bringing Israel out of bondage—set the context, the foundation, for the giving of the law. Clearly, it is not God's definition of right and wrong that keeps us in bondage; the law was given as a guide to the right way to live. The "bondage" that we are subject to derives from Satan (Ephesians 2:1-3; 6:12; II Corinthians 4:4; Revelation 12:9), this world (Exodus 6:5-8; Deuteronomy 5:6), sin (John 8:33-36), and our own human nature—our carnal mind and heart. Our bondage is to sin (John 8:33-34)—not to God's definition of it.
The Old Covenant did not provide a way to overcome these things. Even though the Old Covenant included God's royal law of liberty, it had no provision for ever truly escaping the clutches of sin. God's law, which is also a part of the New Covenant (Hebrews 8:7-12; Jeremiah 31:31-34), merely defines what sin is, so that one may avoid it (Romans 3:20; 4:14-15; 5:13; 7:7, 12, 14). It neither enslaves, nor frees. The Old Covenant—the agreement, rather than the law that was its core—provided no means for overcoming the evil heart of unbelief (Hebrews 3:12, 19; 8:7-8), and so Paul compares it to a bondwoman. In verse 24 he says that it "engenders"—gives birth to—bondage. He does not mean that the agreement between God and Israel was bondage, nor that God's definition of right and wrong keeps people in slavery, but rather that the temporary covenant made no provision for true spiritual freedom. It "gave birth to" bondage because, without addressing the incurable sickness of the heart, the only possible outcome was human degeneration back into the bondage from which they had been freed.
The New Covenant addresses these problems:
For if that first covenant had been faultless, then no place would have been sought for a second. Because finding fault with them [the weakness was with the people, not the agreement or the law], He says: "Behold, the days are coming, says the LORD, when I will make a new covenant with the house of Israel and with the house of Judah—not according to the covenant that I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt; because they did not continue in My covenant, and I disregarded them, says the LORD. For this is the covenant that I will make with the house of Israel after those days, says the LORD: I will put My laws in their mind and write them on their hearts; and I will be their God, and they shall be My people. None of them shall teach his neighbor, and none his brother, saying, 'Know the LORD,' for all shall know Me, from the least of them to the greatest of them. For I will be merciful to their unrighteousness, and their sins and their lawless deeds I will remember no more." (Hebrews 8:7-12; see Jeremiah 31:31-34)
The New Covenant allows God's way of life (law) to be internalized (put into the mind and heart). It allows for a personal relationship with God, rather than going through an intermediary. It allows for complete forgiveness of sins through repentance and accepting the shed blood of Jesus Christ.
In another place, God promises,
Then I will give them one heart, and I will put a new spirit within them, and take the stony heart out of their flesh, and give them a heart of flesh, that they may walk in My statutes and keep My judgments and do them; and they shall be My people, and I will be their God. (Ezekiel 11:19-20)
Through the justification and forgiveness of sins available under the New Covenant, it is possible for the heart to be changed, and for human nature, which drives us to sin, to be overcome. Thus, true spiritual freedom is offered under the New Covenant, while absent under the Old.
David C. Grabbe
He gives us this example and then specifically tells us that what is seemingly a simple historical narrative is actually an allegory. In other words, as important as the story is in its effect on the continuation of the promises, it also has continuous application in certain spiritual circumstances. What at first seems only to be an interesting historical reference has a dual use. Much of the Old Testament fits this usage, providing us with valuable spiritual instruction through its examples.
John W. Ritenbaugh
The Offerings of Leviticus (Part One): Introduction
Webster's Dictionary defines allegory as "to speak figuratively, a symbolic representation." Unger's Bible Dictionary defines it as expressing or explaining one thing under the image of another and showing a second and deeper meaning than would seem apparent. Again, it is similar to a parable.
Paul—addressing the New Testament church, which he calls "the Israel of God" (Galatians 6:16)—shows that the Old Covenant points to and helps explain the New. He writes that Jerusalem is a figure, forerunner, type, and present-day symbol of the New Covenant and church today (see also Hebrews 12:22-23, Romans 9:1-8; I Peter 2:9). We can then read both the history and prophecy regarding Jerusalem, the physical capital of Israel, and apply much of it to the church, the spiritual "Jerusalem, . . . mother of us all."
Other Forerunner Commentary entries containing Galatians 4:24:
2 Kings 4:8-37