So, we gentiles are in a bind. On the one hand, the Jews are "enemies of the gospel", and yet their enmity was the price of gentile salvation. Christians must be wary of attacks on the gospel, yet they must love the attacker because without the attacks we wouldn't have been saved.
Paul also makes it clear that this is a great "mystery." I think that he's saying here, in effect, "Nobody is more surprised by the Jewish rejection of Christ as me, Paul. But I've seen after all these years that their rejection is a hidden part of God's plan of salvation for you gentiles. So be glad that Jews have rejected Christ, and while taking care to keep the faith pure, love the Jews as the apple of God's eye." Not an easy thing, but I think it's what Paul was saying all along.
I am reminded of Jesus’ words, I think about Luke 20, “you’ll not see me again until you say ‘Blessed is He who comes in the name of the Lord.’”