How did Roberto make a difference in the world in the book Stones in Water?

Stones in Water is a novel written by Donna Jo Napoli. It takes place in the early 1940s, during World War II, when Nazi rule and soldiers were present in many European countries. It is a story about a group of young boys who face the obstacles of surviving the harsh treatment of the German soldiers. Roberto, who is a Catholic, is a friend of Samuele, who is called "Enzo" to try to avoid being detected as a Jew. Ultimately, the Nazis find out that Samuele is Jewish due to his circumcision, and he is eventually killed. Roberto, after witnessing Enzo's death, develops maturity and courage to fight on and make a difference in the world.
Specifically, Roberto decides to return to Italy, where he can join the partisans (partigianos) and do his part to attempt to put an end to Nazi occupation and the war. This happens near the end of the story, which is when Roberto's compassion and humanity truly shine. He promises to help other Jews who are facing persecution and torture at the hands of the Nazis or anyone else. He strives to help the Jews escape and be free from the reign of terror and death that the Nazis and other groups in society perpetrate.