The commandment of "Do not stand idly by the blood of your neighbor" which means that if someone's life is in danger of death, you are commanded to save them. 

After being mortally stabbed from behind, he did whatever he could to make sure the terrorist didn't harm anyone around him, in fact he saved a woman's life in the process. He not only lived up to the mitzvah but also to his own words (pictured). 

It is not easy to do what he did, in fact most people wouldn't have reacted the way that he did considering how serious his injury was.

May his memory be blessed

Source: Documentinig Israel