Okay kiddo, let me explain. Pope Pius XI was a really important guy who was in charge of the Catholic Church a long time ago. He believed that everyone should be treated equal and loved no matter how different they were.
Now, Judaism is a religion that many people practice. But a long time ago, some people didn't treat Jewish people very kindly. They were not fair and didn't show love for them. This made the Pope very sad because he believed that everyone should be treated with kindness and respect.
So, Pope Pius XI tried to change things. He met with Jewish leaders to show them love and support. He also wrote letters to Catholics all around the world telling them that they should love and respect Jewish people just like they would any other person.
Although not everyone agreed with the Pope's ideas, he worked really hard to spread love and kindness in the world. And that, my dear, is what we call an act of love and kindness towards all people, regardless of their religion or background.