It shows ancestry according to the flesh.
In a certain case for Israel, yes. For Gentiles no.
Scripture specifically teaches that we are spiritual children to Abraham, you can look that up, and read it.
Yes, including believers of the seed of Israel too. I've been quoting that idea from Gal.3 from Apostle Paul. Haven't you been reading my posts?
Those in Christ Jesus are ALL... spiritual children of Abraham. You know why? Because God's Salvation Promise by 'Faith' (The Gospel) was first offered through Abraham, and it continued among the believing seed of Israel and then was taken to the Gentiles. It never was a Salvation by 'seed' doctrine. Even those born of Israel MUST believe on Jesus of Nazareth as The Christ to be saved.
God made promises that these would father many nations. And God said of one of those, this is in our faith, that we are the children of faithful Abraham.
Not exactly, because if that were true, then God's Salvation would be about Salvation by birth, and not by Faith on The Promise (Gospel). It's The Gospel which Abraham believed by Faith, which is 'how' we have become the children of Abraham.
Paul is more direct here as to what our Faith is in relation to Abraham's Faith...
Gal 3:14
14 That the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith.
KJV
Paul explains the blessing there, what it is. It's the receiving of The Spirit through Faith on Jesus Christ. That's The Gospel of Jesus Christ, and Jesus said at the end of John 8 that Abraham saw His day, and rejoiced. So Abraham knew more of The Gospel than just God saying he would be the flesh father of many nations. The application was especially meant within The Gospel of Jesus Christ by Faith. So who all does that include? And so it has been like God said.
The Bible never makes the same statement regarding Isaac or Jacob, but is as silent on the topic as it is clear concerning Abraham.
That's an area you might want to study more, because The Old Testament Books does say more than you think about Isaac and Jacob's place in The Gospel, especially with Jacob. By that study you will discover many of the same blessings first given to Abraham passed down to his son Isaac, and then to his son Jacob. It's about God's Birthright, the Birthright that the Islamic clerics are still jealous of the Jews over today, because they claim Ishmael was the true firstborn of Abraham (he was, but not of Abraham and Sarah which God had before promised an heir, which would be Isaac). And what's funny, is that the majority of Jews today still reject Jesus of Nazareth as The Christ, and thus The Gospel Promise by Faith first given through Abraham.
Remember, that you can have a nation continuing on through history, and those who leave those people early on, and begin their own nations, and you may have any number of people groups that have thier origin in Abraham, Isaac, Jacob, Ephraim, whomever.
You're veering off track. God's Word is specific on this matter. You simply haven't studied it or haven't understood it yet.
To me it seems a needless assumption that God was speaking of more than the same promise of descendants.
You apparently don't realize that above statement is arguing with God on the matter, not with me. If you don't understand this matter, put it on a shelf and pray about it. But don't mock it, because the "company of nations" and "multitude of nations" prophecies are indeed about the literal seed of Israel, just not in the holy lands. Ask Keraz, as he understands where I'm coming from about this.