Romans 11:1-5 :
"I say then, Hath God cast away his people? God forbid. For I also am an Israelite, of the seed of Abraham, of the tribe of Benjamin. God hath not cast away his people which he foreknew. Wot ye not what the scripture saith of Elias? how he maketh intercession to God against Israel, saying, Lord, they have killed thy prophets, and digged down thine altars; and I am left alone, and they seek my life. But what saith the answer of God unto him? I have reserved to myself seven thousand men, who have not bowed the knee to the image of Baal. Even so then at this present time also there is a remnant according to the election of grace.
According to Paul, God does not forsake Israel, his people.
And that is true that God has not and will not ever forsake his chosen people. The problem is that most people assume wrongly that flesh descendants of Israel are God's chosen people but they're not. Paul fits both categories because he was a flesh descendant and he was also a spiritual descendant.
In the later part of Romans 10 God is casting away the flesh descendants of Israel and turning the kingdom over to the gentiles.
In Romans 11 Paul is saying that although God is casting away the flesh descendants of Israel, he is in no way casting away his chosen people out of Israel just because they are flesh descendants.
Rom 10:16 But they have not all obeyed the gospel. For Esaias saith, Lord, who hath believed our report?
Rom 10:17 So then faith cometh by hearing, and hearing by the word of God.
Rom 10:18 But I say, Have they not heard? Yes verily, their sound went into all the earth, and their words unto the ends of the world.
Rom 10:19 But I say, Did not Israel know? First Moses saith, I will provoke you to jealousy by them that are no people, and by a foolish nation I will anger you.
Rom 10:20 But Esaias is very bold, and saith, I was found of them that sought me not; I was made manifest unto them that asked not after me.
Rom 10:21 But to Israel he saith, All day long I have stretched forth my hands unto a disobedient and gainsaying people.
Rom 11:1 I say then, Hath God cast away his people? God forbid. For I also am an Israelite, of the seed of Abraham, of the tribe of Benjamin.
Rom 11:2 God hath not cast away his people which he foreknew. Wot ye not what the scripture saith of Elias? how he maketh intercession to God against Israel, saying,