3 For I could wish that I myself were accursed—cut off from Christ—for the sake of my people, my fellow countrymen, 4 who are Israelites. To them belong the adoption as sons, the glory, the covenants, the giving of the law, the temple worship, and the promises. 5 To them belong the patriarchs, and from them, by human descent, came the Christ, who is God over all, blessed forever! Amen. 6 It is not as though the word of God had failed. For not all those who are descended from Israel are truly Israel, 7 nor are all the children Abraham’s true descendants; rather “through Isaac will your descendants be counted.” 8 This means it is not the children of the flesh who are the children of God; rather, the children of promise are counted as descendants.
Mishnah Sanhedrin 10Mishnah
All of the Jewish people, even sinners and those who are liable to be executed with a court-imposed death penalty, have a share in the World-to-Come, as it is stated: “And your people also shall be all righteous, they shall inherit the land forever; the branch of My planting, the work of My hands, for My name to be glorified” (Isaiah 60:21). And these are the exceptions, the people who have no share in the World-to-Come, even when they fulfilled many mitzvot: One who says: There is no resurrection of the dead derived from the Torah, and one who says: The Torah did not originate from Heaven, and an epikoros, who treats Torah scholars and the Torah that they teach with contempt. Rabbi Akiva says: Also included in the exceptions are one who reads external literature, and one who whispers invocations over a wound and says as an invocation for healing: “Every illness that I placed upon Egypt I will not place upon you, for I am the Lord, your Healer” (Exodus 15:26). By doing so, he shows contempt for the sanctity of the name of God and therefore has no share in the World-to-Come. Abba Shaul says: Also included in the exceptions is one who pronounces the ineffable name of God as it is written, with its letters.
Notes and References
"... As an expression pertaining to the salvation of Israel but not necessarily every individual Jew, pas Israel in 11:26 suggests that the nation is to be understood as a corporate entity, in which the present division between Jewish "believers" and "unbelievers" as groups within Israel will be removed. Although the writer of the Testament of Benjamin does not explain what he means by the use of this expression, it appears that he, too, may understand "Israel" in 10:11 primarily as a corporate body. If this is correct, the emphasis is on the corporateness rather than the individuality of the members of the nation and on the extensiveness of that which is being described. This may be reflected also in the frequently cited reference to Mishnah Sanhedrin 10:1. In this text, "all Israel" is said to have a share in the world to come; but following this statement a list of those who do not have a share is given. As this tradition has been included in the Mishnah, there is apparently thought to be no contradiction between the claim that "all Israel" has a share in the world to come and the listing of those who are excluded ..."
Aageson, James W. Paul's Use of Scripture: A Comparative Study of Biblical Interpretation in Early Palestinian Judaism and the New Testament With Special Reference to Romans 9-11 (pp. 270-271) Mansfield College, the University of Oxford, 1983