Romans 9:7-9

7and not all are children of Abraham abecause they are his offspring, but bThrough Isaac shall your offspring be named.” 8This means that it is not the children of the flesh who are the children of God, but cthe children of the promise are counted as offspring. 9For this is what the promise said: dAbout this time next year I will return, and Sarah shall have a son.”

Galatians 4:22-26

22For it is written that Abraham had two sons, eone by a slave woman and fone by a free woman. 23But gthe son of the slave was born according to the flesh, while hthe son of the free woman was born through promise. 24Now this may be interpreted allegorically: these women are two icovenants. jOne is from Mount Sinai, bearing children for slavery; she is Hagar. 25Now Hagar is Mount Sinai in Arabia;
Some manuscripts For Sinai is a mountain in Arabia
she corresponds to the present Jerusalem, for she is in slavery with her children.
26But lthe Jerusalem above is free, and she is our mother.
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