'Descendants' in the Bible

Therefore, [inheriting] the promise depends entirely on faith [that is, confident trust in the unseen God], in order that it may be given as an act of grace [His unmerited favor and mercy], so that the promise will be [legally] guaranteed to all the descendants [of Abraham]—not only for those [Jewish believers] who keep the Law, but also for those [Gentile believers] who share the faith of Abraham, who is the [spiritual] father of us all—

In hope against hope Abraham believed that he would become a father of many nations, as he had been promised [by God]: “So [numberless] shall your descendants be.”

and they are not all the children of Abraham because they are his descendants [by blood], but [the promise was]: “Your descendants will be named through Isaac” [though Abraham had other sons].

That is, it is not the children of the body [Abraham’s natural descendants] who are God’s children, but it is the children of the promise who are counted as [Abraham’s true] descendants.

It is as Isaiah foretold,“If the Lord of Hosts had not left us seed [future generations from which a believing remnant of Israelites came],We would have become like Sodom, and would have resembled Gomorrah [totally rejected and destroyed]!”