Galatians 4:21-23 Part 2 of 2

Tell me, you who want to be under the law, are you not aware of what the law says? For it is written that Abraham had two sons, one by the slave woman and the other by the free woman. His son by the slave woman was born according to the flesh, but his son by the free woman was born as the result of a divine promise.

For it is written that Abraham had two sons, one by the slave woman 
Genesis 16:15  So Hagar bore Abram a son, and Abram gave the name Ishmael to the son she had borne.

and the other by the free woman 
Genesis 21:2  Sarah became pregnant and bore a son to Abraham in his old age, at the very time God had promised him.

His son by the slave woman was born according to the flesh 
Galatians 4:28-29  Now you, brothers and sisters, like Isaac, are children of promise. At that time the son born according to the flesh persecuted the son born by the power of the Spirit. It is the same now.
Romans 9:6-8  It is not as though God's word had failed. For not all who are descended from Israel are Israel. Nor because they are his descendants are they all Abraham's children. On the contrary, "It is through Isaac that your offspring will be reckoned." (Genesis 21:12) In other words, it is not the children by physical descent who are God's children, but it is the children of the promise who are regarded as Abraham's offspring.

but his son by the free woman was born as the result of a divine promise 
Genesis 17:19  Then God said, "Yes, but your wife Sarah will bear you a son, and you will call him Isaac. I will establish my covenant with him as an everlasting covenant for his descendants after him."
Genesis 18:14  "Is anything too hard for the LORD? I will return to you at the appointed time next year, and Sarah will have a son."
Genesis 21:1-2  Now the LORD was gracious to Sarah as he had said, and the LORD did for Sarah what he had promised. Sarah became pregnant and bore a son to Abraham in his old age, at the very time God had promised him.
Hebrews 11:11  And by faith even Sarah, who was past childbearing age, was enabled to bear children because she considered him faithful who had made the promise.

(parentheses are mine)

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