Paul explains that those who trust in Christ are spiritual children of Abraham - they are justified by their faith and share in the covenant blessing God promised to Abraham.

Galatians 3:6–9

6 just as Abraham “believed God, and it was counted to him as righteousness”?

7 Know then that it is those of faith who are the sons of Abraham. 8 And the Scripture, foreseeing that God would justify¹ the Gentiles by faith, preached the gospel beforehand to Abraham, saying, “In you shall all the nations be blessed.” 9 So then, those who are of faith are blessed along with Abraham, the man of faith.

Footnotes

[1] 3:8 Or count righteous; also verses 11, 24

(ESV)