Neither because they are the seed of Abraham
The Jews highly valued themselves, upon being the natural seed of Abraham; and fancied, upon this account, that they were children, which the apostle here denies: neither
are they all children;
as in the former verse, he explains in what sense they were Israelites, which he had mentioned among their high characters and privileges, as descending from Jacob, and in what sense they were not; so in this he shows in what manner the "adoption", ( Romans 9:4 ) , belonged to them, and it did not; being Abraham's seed, they were his natural children, and the children of God by national adoption; but, they were not all the spiritual children of Abraham, nor the children of God by the special grace of adoption; these characters only belonged to some of them, and which are equally true of Gentile believers; who being of the same faith with Abraham, are his children, his seed, and also the children of God: natural descent from Abraham avails nothing in this case, as is clear from the instance of Ishmael and Isaac. Ishmael was the natural seed of Abraham, as well as Isaac; but he was not a son of Abraham in a spiritual sense, nor a child of God; he was not a child of promise, this was peculiar to Isaac:
but in Isaac shall thy seed be called;
see ( Genesis 21:12 ) . The meaning of which is, either that the progeny of Abraham in the line of Isaac should only be called, accounted, and esteemed, in an eminent sense, the seed of Abraham, and not his posterity in the line of Ishmael: agreeably to which the Jews say F3, that
``Ishmael is not (Mhrba lv werz llkb) , "in the general account of the seed of Abraham"; for it is said, "in Isaac shall thy seed be called", ( Genesis 21:12 ) ; nor is Esau in the general account of the seed of Isaac; hence, says R. Joden bar Shalom, in Isaac, that is, in part of Isaac.''So another F4 of their writers, on mentioning this passage, observes,
``that it is said in Isaac, (qxuy lk alw) , but "not all Isaac";''or all that sprung from him. Or this has respect to the most eminent and famous seed of Abraham, the Messiah, in whom all nations of the earth were to be blessed; who was to spring from him by Isaac, in the line of Jacob; and may likewise have a personal respect to Isaac himself, the son of the promise, a child of Abraham in a spiritual sense, when Ishmael was not; and to whom belonged the spiritual promises and blessings, and who was to be, and was effectually called by the grace of God; and may include also his whole seed and posterity, who, both natural and spiritual, were children of the typical promise, the land of Canaan, and the enjoyment of temporal good things; and the matter also children of the antitypical promise, or of those spiritual and eternal things, which God has promised to Abraham's spiritual seed, whether among Jews or Gentiles; and which always have their effect, and had, even when, and though Abraham's natural seed had a "lo ammi", ( Hosea 1:9 ) , written upon them.
F3 T. Hieros. Nedarim, fol. 38. 1.
F4 Yom Tob in Misn. Bava Metzia, c. 7. sect. 1.