Romans 9:8

This means that it is not the children of the flesh who are the children of God , but the children of the promise are counted as offspring .

In other words, it is not the children by physical descent who are God`s children, but it is the children of the promise who are regarded as Abraham`s offspring.

That is, They which are the children of the flesh, these are not the children of God : but the children of the promise are counted for the seed.