Rom 11 says "God is able to graft them in again IF they do not continue in unbelief".
IT also says "you stand by your faith.. you should fear for if God did not spare them he may not spare you either... to you God's mercy and goodness IF you continue"
There was a specific hardening of those particular Jews who, despite Jesus having been performing miracles proving himself right before their eyes, would still not believe: "The Jews [i.e., the leaders of the Jews] then gathered around Him, and were saying to Him, 'How long will You keep us in suspense? If You are the (Messiah), tell us plainly.' Jesus answered them, 'I told you, and you do not believe; the [miracles] that I do in My Father's name, these testify of Me. But you do not believe because you are not of My sheep. My sheep hear My voice, and I know them, and they follow Me.'" John 10:24-27
And so: "Though He had performed so many signs before them, yet [most of the leaders of the Jews] were not believing Him... [And because they would not believe Him] they could [never] believe, for Isaiah said again, 'He has blinded their eyes and He hardened their heart, so that they would not see with their eyes and perceive with their heart, and be converted and I heal them.'" John 12:37-40. The Jewish leadership did not "recognize the time of (their) visitation," Luke 19:44, because they did not want to lose their positions of power and places of honor.
That is the hardening of Romans 11:7-10. God still held out the possibility to even those who saw but would not believe during that generation, and Paul wished those branches might even be grafted back in again.
But there is a "
mystery" (something previously unheard of but now revealed) of a "
partial hardening" of Israel that continues for that people group
from that time "until the fullness of the Gentiles has come in," Romans 11:25-30. That is the
partial hardening of the Jews of Judaism of the last two millennia, which hardening is removed when "the Deliverer will come (to) Zion, (when) He will remove ungodliness from Jacob," Romans 11:26, for the "times of the Gentiles" is completed when the Son of Man returns to earth in His "great glory," Luke 21:24-27.
That partial hardening of Israel -- the Jews of Judaism -- by God is done for two God-reasons: 1) "
their rejection is the reconciliation of the world" (i.e., the gospel goes out to the whole world) (Romans 11:11-15), and 2) so God may fulfill all the promises He made to national Israel, restoration to the Land, building of the Temple, setting His King upon the throne of David to rule all the nations of the earth in righteousness and peace, for "
from the standpoint of God's choice they are beloved for the sake of the [promises made to their] fathers," (Romans 11:28).
That is why Paul commands us Gentile Christians not to be arrogant to the natural branches of the Olive Tree, the Jews of Judaism. They remain under the veil of the old covenant, just as Moses was in his day.