The Jewish covenant was to those born of Jewish parents. The Christian one is to those born again...
” Note this carefully. We began by saying that Abraham’s faith was counted unto him for righteousness. When this happened, was he a circumcised man? He was not, he was still uncircumcised. It was afterwards that the sign of circumcision was given to him, as a seal upon that righteousness which God was accounting to him as yet an uncircumcised man! God’s purpose here is twofold. First, that Abraham might be the spiritual father of all who since that time, despite their circumcision, show the faith that is counted as righteousness. Then, secondly, that he might be the circumcised father of all those who are not only circumcised, but are living by the same sort of faith which he himself had before he was circumcised...
...Now this counting of faith for righteousness was not recorded simply for Abraham’s credit, but as a divine principle which should apply to us as well. Faith is to be reckoned as righteousness to us also, who believe in him who raised from the dead our Lord Jesus Christ, who was delivered to death for our sins and raised again to secure our justification.”
Well, technically maybe on the “parents” part, but in reality according to the Law of Moses he who is born of a Jew is a Jew” ~
J.B. Phillips? (Should always give source.) But see http://www.freerepublic.com/focus/religion/2990777/posts?page=19#19 above