Romans 11 was a bit long, so if you want to read the passage, click on the above link.
After all the Paul has said, he wants to make it abundantly clear that he is not saying that God is going to leave the nation of Israel by the wayside. Even in the past, when many Israelites turned away from God and worshipped false idols, there were alwas a few Israelites that remained faithful. So those few that remained faithful were chosen by God and the remaining had their hearts hardened, according to the scriptures. According to scriptures, God turned his favor onto the Gentiles (non-Jews) and many of them were saved. Paul is one of the chief apostles to the Gentiles, sharing the Word with them and encouraging them on to having a relationship with Jesus. Paul is hopeful that the relationship that the Gentiles have with God will make the Jews jealous and push them over to accepting Jesus. He does not think the Jews are lost.
The last point is almost a scary point to me because Paul says that the Jews were pruned off of the vine to make room for new branches, metaphorically speaking. But just as easily as the non-believers were pruned off, this could also happen to believers who stop believing (this is at least how I am reading it and understanding it). The cool thing, though, is that if you believe in God and His kindness, you will receive His kindness. And if you turn away, you will receive His judgement.