[Gal 4:21-31 NASB]
21 Tell me, you who want to be under law, do you not listen to the law? 22 For it is written that Abraham had two sons, one by the bondwoman and one by the free woman. 23 But the son by the bondwoman was born according to the flesh, and the son by the free woman through the promise. 24 This is allegorically speaking, for these [women] are two covenants: one [proceeding] from Mount Sinai bearing children who are to be slaves; she is Hagar. 25 Now this Hagar is Mount Sinai in Arabia and corresponds to the present Jerusalem, for she is in slavery with her children. 26 But the Jerusalem above is free; she is our mother. 27 For it is written, "REJOICE, BARREN WOMAN WHO DOES NOT BEAR; BREAK FORTH AND SHOUT, YOU WHO ARE NOT IN LABOR; FOR MORE NUMEROUS ARE THE CHILDREN OF THE DESOLATE THAN OF THE ONE WHO HAS A HUSBAND." 28 And you brethren, like Isaac, are children of promise. 29 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 also. 30 But what does the Scripture say? "CAST OUT THE BONDWOMAN AND HER SON, FOR THE SON OF THE BONDWOMAN SHALL NOT BE AN HEIR WITH THE SON OF THE FREE WOMAN." 31 So then, brethren, we are not children of a bondwoman, but of the free woman.
[Gen 21:10-13 NASB]
10 Therefore she said to Abraham, "Drive out this maid and her son, for the son of this maid shall not be an heir with my son Isaac." 11 The matter distressed Abraham greatly because of his son. 12 But God said to Abraham, "Do not be distressed because of the lad and your maid; whatever Sarah tells you, listen to her, for through Isaac your descendants shall be named. 13 "And of the son of the maid I will make a nation also, because he is your descendant."
[Gen 17:4-7, 18-21 NASB]
4 "As for Me, behold, My covenant is with you, And you will be the father of a multitude of nations. 5 "No longer shall your name be called Abram, But your name shall be Abraham; For I have made you the father of a multitude of nations. 6 "I will make you exceedingly fruitful, and I will make nations of you, and kings will come forth from you. 7 "I will establish My covenant between Me and you and your descendants after you throughout their generations for an everlasting covenant, to be God to you and to your descendants after you. ... 18 And Abraham said to God, "Oh that Ishmael might live before You!" 19 But God said, "No, but Sarah your wife will bear you a son, and you shall call his name Isaac; and I will establish My covenant with him for an everlasting covenant for his descendants after him. 20 "As for Ishmael, I have heard you; behold, I will bless him, and will make him fruitful and will multiply him exceedingly. He shall become the father of twelve princes, and I will make him a great nation. 21 "But My covenant I will establish with Isaac, whom Sarah will bear to you at this season next year."
So we see that God says that Ishmael (who represents
The Law allegorically) will become a great nation (singular) with 12 princes, while Isaac (representing the covenant of faith) will be the sole heir and will become many nations. Allegorically, Ishmael represents Judaism, while Isaac represents Christianity.... Ishmael represents the physical descendants of Abraham (the Hebrews), while Isaac represents the spiritual descendants of Abraham (those with faith in the gospel of Christ).