For the promise that he would inherit the world did not come to Abraham or to his descendants through the Law, but through the righteousness produced by faith.

For if those who were given the Law are the heirs, then faith is useless and the promise is worthless,

Therefore, the promise is based on faith, so that it may be a matter of grace and may be guaranteed for all of Abraham's descendants not only for those who were given the Law, but also for those who share the faith of Abraham, who is the father of us all.

nor did he doubt God's promise out of a lack of faith. Instead, his faith became stronger and he gave glory to God,

That is, it is not merely the children born through natural descent who were regarded as God's children, but it is the children born through the promise who were regarded as descendants.

For this is the language of the promise: "At this time I will return, and Sarah will have a son."