Galatians 3:16
Now the promises were made to Abraham and his line. It does not say, "and to your lines," in the plural, but in the singular, "and to your line," that is, Christ.
Romans 9:8
That is to say, it is not his physical descendants who are children of God, but his descendants born in fulfilment of the promise who are considered his true posterity.
Galatians 4:28
Now we, brothers, are like Isaac, children born in fulfilment of the promise.
Hebrews 11:13
All these people lived all their lives in faith, and died without receiving what had been promised; they only saw it far ahead and welcomed the sight of it, recognizing that they themselves were only foreigners and strangers here on earth.