Israel and the church
'All Israel will be saved' beside the kingdom taken from the tenants — remnant, national restoration and supersessionist readings of Israel and the church.
Romans 11:25-29
25For I don’t desire you to be ignorant, brothers, of this mystery, so that you won’t be wise in your own conceits, that a partial hardening has happened to Israel, until the fullness of the Gentiles has come in,
26and so all Israel will be saved. Even as it is written, “There will come out of Zion the Deliverer, and he will turn away ungodliness from Jacob.
27This is my covenant with them, when I will take away their sins.”
28Concerning the Good News, they are enemies for your sake. But concerning the election, they are beloved for the fathers’ sake.
29For the gifts and the calling of God are irrevocable.
Matthew 21:43
43“Therefore I tell you, God’s Kingdom will be taken away from you, and will be given to a nation producing its fruit.
What each tradition says
Rabbinic / Midrashic
Kohler states that the Pauline school, writing under Paul's name but scarcely Paul himself, worked out a theory based on Jeremiah 31:30-31. According to it, the Church of Christ represents the new covenant in place of the old, citing Romans 11:27, Galatians 4:24, Hebrews 8:6-13; 9:15-10:17, and 1 Corinthians 11:23-28.
Kaufmann Kohler (1843-1926), The Jewish Encyclopedia (New York: Funk & Wagnalls, 1901-1906), s.v. 'Saul of Tarsus' — section 'The Old Testament and the New'
Patristic
Augustine says the apostle himself declares that the Jews who would not believe in Christ were branches broken off. The Gentiles, a wild olive tree, were grafted into the good olive, that is, the holy stock of the Hebrews, that they might partake of the fatness of the olive.
Augustine of Hippo (354-430), Reply to Faustus the Manichaean (trans. Richard Stothert), in Nicene and Post-Nicene Fathers, ser. 1, vol. 4 (ed. Philip Schaff; New York: Christian Literature Publishing Co., 1890) — Book IX, §2 (on Romans 11:16-26)
Catholic
Merk states that Israel's unbelief is the salvation of the pagan world, and it is likewise a solemn exhortation to fidelity in the faith. He adds that Israel's rejection is not irrevocable: the people will find mercy and salvation.
A. Merk, The Catholic Encyclopedia, s.v. 'Romans, Epistle to the' (New York: Robert Appleton Company, 1912) — outline of the epistle, section on ix. 1-xi. 36
Orthodox
Chrysostom explains that the “allayment” is this: when the fulness of the Gentiles has come in, then all Israel will be saved. He places this salvation at the time of his second coming and the end of the world.
John Chrysostom (c. 349-407), Homilies on the Epistle to the Romans, in Nicene and Post-Nicene Fathers, ser. 1, vol. 11 (ed. Philip Schaff; T&T Clark, Edinburgh, 1889) — Homily XIX, on Romans 11
Reformed / Protestant
Calvin extends Israel to all God's people, not only the Jews. When the Gentiles come in, the Jews also return from their defection to the obedience of faith. Thus the salvation of the whole Israel of God is completed, gathered from both, with the Jews first, as it were God's first-born.
John Calvin (1509-1564), Commentaries on the Epistle of Paul the Apostle to the Romans (trans. John Owen; Edinburgh: Calvin Translation Society, 1849) — commentary on Romans 11:26
Evangelical
Wesley says all Israel shall be saved, being convinced by the coming of the Gentiles. He adds that there will be a still larger harvest among the Gentiles when all Israel is come in.
John Wesley (1703-1791), Explanatory Notes upon the New Testament (1755), in Wesley's Notes on the Bible (CCEL) — note on Romans 11:26