Because Abraham was saved by faith (and not works of the law), the same is surely true of Israel. God did not repeal his promises to Abraham when the Law of Moses came into effect and then reinstate his promises to Abraham when Jesus died on the cross. The promises made to Abraham remained continuously in effect.
For example, in the Torah, God explicitly says he chose Israel to be saved because of his covenant with Abraham –
(Lev. 26:40-42 ESV) “But if they confess their iniquity and the iniquity of their fathers in their treachery that they committed against me, and also in walking contrary to me, 41 so that I walked contrary to them and brought them into the land of their enemies – if then their uncircumcised heart is humbled and they make amends for their iniquity, 42 then I will remember my covenant with Jacob, and I will remember my covenant with Isaac and my covenant with Abraham, and I will remember the land.”
(Deu 9:5-6 ESV) Not because of your righteousness or the uprightness of your heart are you going in to possess their land, but because of the wickedness of these nations the LORD your God is driving them out from before you, and that he may confirm the word that the LORD swore to your fathers, to Abraham, to Isaac, and to Jacob. 6 “Know, therefore, that the LORD your God is not giving you this good land to possess because of your righteousness, for you are a stubborn people.
And the OT has countless passages that speak of God’s salvation in terms of believing in God or trusting God.
(Exo 4:30-31 ESV) Aaron spoke all the words that the LORD had spoken to Moses and did the signs in the sight of the people. 31 And the people believed; and when they heard that the LORD had visited the people of Israel and that he had seen their affliction, they bowed their heads and worshiped.
(Psa 40:4 ESV) Blessed is the man who makes the LORD his trust, who does not turn to the proud, to those who go astray after a lie!
(Psa 84:12 ESV) O LORD of hosts, blessed is the one who trusts in you!
(Psa 125:1 ESV) Those who trust in the LORD are like Mount Zion, which cannot be moved, but abides forever.
(Psa 146:5 ESV) Blessed is he whose help is the God of Jacob, whose hope is in the LORD his God,
(Pro 16:20 ESV) Whoever gives thought to the word will discover good, and blessed is he who trusts in the LORD.
(2 Chr 20:18-20 ESV) Then Jehoshaphat bowed his head with his face to the ground, and all Judah and the inhabitants of Jerusalem fell down before the LORD, worshiping the LORD. 19 And the Levites, of the Kohathites and the Korahites, stood up to praise the LORD, the God of Israel, with a very loud voice. 20 And they rose early in the morning and went out into the wilderness of Tekoa. And when they went out, Jehoshaphat stood and said, “Hear me, Judah and inhabitants of Jerusalem! Believe in the LORD your God, and you will be established; believe his prophets, and you will succeed.”
(Jer 17:7-8 ESV) “Blessed is the man who trusts in the LORD, whose trust is the LORD. 8 He is like a tree planted by water, that sends out its roots by the stream, and does not fear when heat comes, for its leaves remain green, and is not anxious in the year of drought, for it does not cease to bear fruit.”
(Jer 39:18 ESV) “‘For I will surely save you, and you shall not fall by the sword, but you shall have your life as a prize of war, because you have put your trust in me, declares the LORD.’”
(Hab 2:4 ESV) “Behold, his soul is puffed up; it is not upright within him, but the righteous shall live by his faith.”
This is but a sampling of the many OT verses that speak of salvation for those with faith in or who trust God. After all, the faith shown by Abraham was trust that God would keep his promises. The “trust” passages speak very much to this promise.
The theme of the first four chapters of Ephesians is the unity of Jews and Gentiles made possible by God’s grace. Chapter 1 speaks of God’s election of Israel to be saved and God’s choice to include believing Gentiles among his elect people. Chapter 2 explains that God does this by saving us by faith, not works – allowing him to include Gentiles among the saved.
(Eph 3:1-3 ESV) For this reason I, Paul, a prisoner for Christ Jesus on behalf of you Gentiles – 2 assuming that you have heard of the stewardship of God’s grace that was given to me for you [Gentiles], 3 how the mystery was made known to me by revelation, as I have written briefly.
This is a complex sentence. We need to follow its contours closely. Paul introduces the idea of a “mystery” disclosed to him by God.
(Eph 3:4-5 ESV) When you read this, you can perceive my insight into the mystery of Christ, 5 which was not made known to the sons of men in other generations as it has now been revealed to his holy apostles and prophets by the Spirit.
This mystery is now a revelation. It was hidden in the past but is now revealed through the apostles and prophets.
(Eph 3:6 ESV) This mystery is that the Gentiles are fellow heirs, members of the same body, and partakers of the promise in Christ Jesus through the gospel.
The mystery now revealed is that the Gentiles are “fellow heirs” (co-inheritors) of the promise that comes through Jesus by the gospel. That the Jews were to receive the gospel was no secret. The OT prophets had been very clear on this point. The newly revealed truth is the inclusion of the Gentiles among the Jews without distinction and without having to become Jews to be saved.
(Eph 2:11-16 ESV) Therefore remember that at one time you Gentiles in the flesh, called “the uncircumcision” by what is called the circumcision [the Jews], which is made in the flesh by hands – 12 remember that you were at that time separated from Christ, alienated from the commonwealth of Israel and strangers to the covenants of promise, having no hope and without God in the world. 13 But now in Christ Jesus you [Gentiles] who once were far off have been brought near by the blood of Christ. 14 For he himself is our peace, who has made us [Jews and Gentiles] both one and has broken down in his flesh the dividing wall of hostility 15 by abolishing the law of commandments expressed in ordinances, that he might create in himself one new man in place of the two, so making peace, 16 and might reconcile us both to God in one body through the cross, thereby killing the hostility.
The Jews have always had the “covenants of promise,” but the Gentiles were without hope – until Jesus changed everything. He broke down the “dividing wall of hostility” joining Jews and Gentiles into a single body.
We often miss one of Paul’s implicit but essential points. The Gentiles are saved because they’ve been added to the same body as the Jews. The Gentiles have now received the covenant promises of the Jews – and so may be saved.
Paul speaks of Jesus as extending the promises to the Gentiles, not as establishing a new promise. Now, there is a difference – a big one – in that the faith required of the Jews has become faith in Jesus as Lord (Rom 10:9). The Jews were saved by faith – but now only by faith in God understood correctly through Jesus. Miss Jesus and you miss God.
Before Jesus, the Jews were asked to believe in a Messiah not yet revealed. After Jesus, they were asked to believe in the revealed Messiah – which became a stumbling block.
And so we have the irony that the Jews largely surrendered promises they already had by rejecting Jesus as Lord – and thereby rejecting God. And yet the promises were extended to the Gentiles, who largely accepted them.