Praise the Lord (Psalms 117:1-2) that it is the spirit that matters not the flesh (John 6:63), that we need not concern ourselves with genealogies (Titus 3:9) for God is not a respecter of persons (Acts 10:34) but of faith, as it is that which He counts for righteousness (Romans 4:5).
Even as Abraham believed God, and it was accounted to him for righteousness. Know ye therefore that they which are of faith, the same are the children of Abraham. (Galatians 3:6-7)
Since Abraham is the father of all those who believe (Romans 4:11-12), we become children of Abraham through our faith and will sit down with him in the kingdom of heaven (Matthew 8:11), while the children of the kingdom (that is, of the physical seed or flesh) will be cast into outer darkness (Matthew 8:12) if they haven’t believed in the name of the only begotten Son of God (John 3:18).
And think not to say within yourselves, We have Abraham to our father: for I say unto you, that God is able of these stones to raise up children unto Abraham. (Matthew 3:9)
In John chapter 8, when Jesus is speaking to the Jews on the Mount of Olives He acknowledges that they are Abraham’s seed (John 8:37) but not Abraham’s children (John 8:39) as they sought to kill him (John 8:40). He further confirms that being the physical seed of Abraham is not what matters when he tells them that God is not their father (John 8:42) but, rather, that they are of their father the devil (John 8:44).
When we are saved by grace through faith (Ephesians 2:8) we are born again in the spirit (John 3:6) and become sons of God (Romans 8:14).
The Spirit itself beareth witness with our spirit, that we are the children of God: And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together. (Romans 8:16-17)
Praise the Lord that it is the spirit that matters not the flesh.