The book the question refers to does not seem to have a correct understanding of the gospel. There is only one gospel which is for both Jews and Gentiles, and Paul clearly taught that.
The beginning of Romans (1:18-3:20) shows that everyone, both Jews and Gentiles, are condemned by their sin. At the very end Paul says what he thought the purpose of the law was:
Obviously, the law applies to those to whom it was given, for its purpose is to keep people from having excuses, and to show that the entire world is guilty before God. For no one can ever be made right with God by doing what the law commands. The law simply shows us how sinful we are. (Romans 3:19-20, NLT)
So "What Torah does for Jews" is condemn them!
What Jesus did, through dying on the cross and coming back to life again, is provide a way for us to receive God's righteousness. This is what the following verses say:
But now God has shown us a way to be made right with him without keeping the requirements of the law, as was promised in the writings of Moses and the prophets long ago. We are made right with God by placing our faith in Jesus Christ. And this is true for everyone who believes, no matter who we are.
For everyone has sinned; we all fall short of God’s glorious standard. Yet God freely and graciously declares that we are righteous. He did this through Christ Jesus when he freed us from the penalty for our sins. For God presented Jesus as the sacrifice for sin. People are made right with God when they believe that Jesus sacrificed his life, shedding his blood. This sacrifice shows that God was being fair when he held back and did not punish those who sinned in times past, for he was looking ahead and including them in what he would do in this present time. God did this to demonstrate his righteousness, for he himself is fair and just, and he declares sinners to be right in his sight when they believe in Jesus. (Romans 3:21-26, NLT)
Several times Paul says very explicitly that the gospel is for both the Jews and Gentiles:
For I am not ashamed of this Good News about Christ. It is the power of God at work, saving everyone who believes—the Jew first and also the Gentile. (Romans 1:16, NLT)
There will be trouble and calamity for everyone who keeps on doing what is evil—for the Jew first and also for the Gentile. But there will be glory and honor and peace from God for all who do good—for the Jew first and also for the Gentile. For God does not show favoritism. (Romans 2:9-11, NLT)