Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall your seed be called.
because.
Luke 3:8 Bring forth therefore fruits worthy of repentance, and begin not to say within yourselves, We have Abraham to our father: for I say unto you, That God is able of these stones to raise up children unto Abraham.
Luke 16:24,25,30 And he cried and said, Father Abraham, have mercy on me, and send Lazarus, that he may dip the tip of his finger in water, and cool my tongue; for I am tormented in this flame…
John 8:37-39 I know that ye are Abraham's seed; but ye seek to kill me, because my word hath no place in you…
In Isaac.
Genesis 21:12 And God said unto Abraham, Let it not be grievous in thy sight because of the lad, and because of thy bondwoman; in all that Sarah hath said unto thee, hearken unto her voice; for in Isaac shall thy seed be called.
Hebrews 11:18 Of whom it was said, That in Isaac shall thy seed be called:
On the contrary, “Through Isaac your offspring will be reckoned.”
This quotation from Genesis 21:12 emphasizes the specific line through which God’s covenant promises would be fulfilled. Isaac, the child of promise, represents the line through which the Messiah, Jesus Christ, would eventually come. This choice of Isaac over Ishmael illustrates the principle of divine election, where God’s purposes are fulfilled according to His sovereign will rather than human expectations. The phrase also connects to the broader theme of God’s faithfulness to His promises, as seen in the fulfillment of the Abrahamic covenant through Isaac’s lineage, ultimately leading to the birth of Christ, who is the fulfillment of the promise to bless all nations through Abraham’s seed (Genesis 12:3).
Paul begins by pointing out that physical lineage alone does not secure covenant status.
• Genesis 12:1–3 shows God promising blessing through Abraham, yet later revelation clarifies the promise is not inherited merely by blood.
• John 8:39 records Jesus telling Jewish listeners, “If you were children of Abraham, you would do the works of Abraham,” highlighting faith, not ancestry, as decisive.
• Matthew 3:9 warns, “And do not presume to say to yourselves, ‘We have Abraham as our father.’”
• Galatians 3:7 concludes, “Understand, then, that those who have faith are sons of Abraham.”
The apostle is setting up a contrast: heritage is a blessing, but not the ultimate criterion God uses.
Paul sharpens the point: God’s family is defined by His promise and calling.
• Romans 2:28–29 notes that “a man is not a Jew because he is one outwardly… but inwardly.”
• 1 John 3:1 speaks of believers being “called children of God,” linking divine declaration with new birth.
• Galatians 3:29 states, “If you belong to Christ, then you are Abraham’s seed,” anchoring identity in Christ.
Thus, “children” equals those who share Abraham’s faith in the promised Messiah, not merely his DNA.
With this phrase Paul pivots to God’s sovereign choice.
• Romans 9:11–12 (in the same chapter) illustrates with Jacob and Esau that God’s purpose stands “not by works but by Him who calls.”
• Romans 11:5 speaks of “a remnant chosen by grace,” sustaining the theme that God actively defines His people.
The words “on the contrary” remind readers that divine election often overturns human expectations.
Quoting Genesis 21:12, Paul shows that God selected Isaac—not Ishmael—to carry the line of promise.
• Hebrews 11:18 repeats the citation, affirming the reliability of God’s Word.
• Galatians 4:22–23 contrasts Ishmael, “born according to the flesh,” with Isaac, “born through the promise,” underscoring God’s initiative.
• Romans 4:16 ties the promise to faith “so that it may be by grace.”
Isaac’s birth illustrates that God’s family is created by supernatural promise, foreshadowing the new birth believers receive in Christ.
Romans 9:7 teaches that belonging to God is not secured by physical descent but by divine promise. Abraham’s true children are those, like Isaac, born as a result of God’s gracious choice and received through faith.
(7) Neither are all the bodily descendants of Abraham also his spiritual descendants. It was expressly stated from the first that the promise was confined to a particular branch of his posterity. The posterity of Abraham, strictly so called, was to be that derived through Isaac. This is very nearly the sense of the original, "In Isaac shall thy seed be called," i.e., in "Isaac shalt thou have posterity, which shall be called thy posterity"--"true and legitimate descendants," thus excluding the seed of Hagar.