Romans 4:13

For it was not through [obedience to] law [See 3:31] that the promise to Abraham or his descendants of inheriting [the best of] the world [was made], but through their being considered righteous because of faith [in God].

Galatians 3:29

And if you belong to Christ, then you are [truly] Abraham's seed [i.e., his spiritual descendants] and thereby [you will] inherit what was promised to him [i.e., God's blessings].

Romans 9:8

This means that it is not the physical descendants [of Abraham] who are God's children, but it is the children [born] according to [God's] promise who are [Abraham's true] descendants.

Galatians 3:16-18

Now [specific] promises were made to Abraham and to his seed [i.e., descendants]. [God] did not say "seeds" [plural] as though He were referring to many persons but "seed" [singular] showing that He meant one [descendant]; [Gen. 13:15 says] "And to your seed," referring to Christ.

Treasury of Scripture Knowledge

Summary

Romans 4:13

For the promise, that he should be the heir of the world, was not to Abraham, or to his seed, through the law, but through the righteousness of faith.

Through the

Galatians 3:16

But through

Romans 4:11

General references

Galatians 4:28

Bible References

Through the

But through

He received the sign of circumcision as a seal [confirming] that he had been [considered] righteous because of the faith he had before being circumcised. Thus, he became the [spiritual] father of all people who believe [in God], even though they have not been circumcised, so that they could be considered righteous [by their faith].

General references

Now, brothers, you [Christians] are children of the promise [made to Abraham. See 3:29] just like Isaac, [Abraham's son] was.