“Israel has experienced a hardening in part until the full number of the Gentiles has come in. And so all Israel will be saved.”...Rom 11:26.
“Though the number of the Israelites be like the sand by the sea, only a remnant will be saved.”...Rom 9:27.
Is there a contradiction here: Rom 11 tells us “all Israel will be saved”, meaning everyone, but Rom 9 tells us “only a remnant will be saved”, meaning only a few?
How do we make sense of these two verses that appear to be a contradiction?
How to make sense of these apparent contradictions? With difficulty.
You have to remember, Paul was not a Christian. He only knows two classes of people, the Jews and the Gentiles. So the first thing to do is forget about Christian theology and apologetics for a while and work from what Paul wrote - not what was written well after his death - which includes the Gospels.
At Rms 3:1-2 says, 'What is the advantage of the Jew? Or what is the value of circumcision? Much in every way'. Clearly Paul indicating that being a Jew is important - but every Jew must keep the law in every way (Gal 56:3). So, for Paul, the Torah remains in effect for all those who are circumcised - Israel's salvation is never in doubt.
In Rms 9 Paul uses a rhetorical device to try to get his point across which is largely lost in the 21st century. He employes a fictitious questioner against who he bounces off arguments and in doing so Paul misleads his reader in order to convince. At Rms 9:19 Paul open the fictitious dialogue, 'But one of you will say to me .... ' But it clear that Paul is not talking to Jews, but to the Gentiles. He clearly says so in v. 24. The following verses are OT scripture which he uses to demonstrate that God is calling those 'who were not my people' - meaning the Gentiles. And just as Isaiah records that God left some Jews behind so too might the same happen to the Gentiles.
We make too much of the perceived inconsistencies in Romans to the point that it is often argued that God has reject the Jews because they have not 'received' Christ. A closer reading of Romans should led us to accept that Paul still maintains his Jewish heritage and sees nothing wrong with the Jews receiving their salvation through adherence to the law. (If 'some are to be rejected' it because of their disobedience to the teachings of the Torah).
Finally, at Rms 15: 18 Paul make his intentions more than clear, 'I will be bold and speak only about what Christ has done through me to lead the Gentiles to obey God'. In his letter to the Romans he talking to Gentiles - not Jews. You have to read his epistle in that light.