"For I could wish that I myself were cursed and cut off from Christ for the sake of my brothers, those of my own race, the people of Israel. Theirs is the adoption as sons; theirs the divine glory, the covenants, the receiving of the law, the temple worship and the promises."
To ask for this, means to ask for a life apart from Christ, eternally cut off from the Father. Paul is willing to give up his salvation. This is crazy.
But what if Christianity isn't about getting into heaven? If it's not about the eternal reward at the end of the long race? If it's not about entering into the Kingdom of God and having your name written in the book of eternal life? From the looks of it, it's about saving everyone else but yourself, and risking life and limb to do so.
Jesus is the first among many heroes. Paul followed suit and many other martyrs even up to this day are dying for the sake of Christ and the gospel. Why? Because it is not their salvation they are after, but that of the world. Christians are heroes.
For Paul, eternal life was on his list of things that could be sacrificed for the sake of his ministry. He was never in it for himself, but for the love of Christ. And we all know that Christ was not in the world for himself, but descended solely for us. Crazy? Yes. Truth? Absolutely. Gospel? 100%.