Ruth was un-Jewish by birth. Moses was un-Jewish by upbringing. But both knew that when they saw suffering and identified with the sufferer, they could not walk away.
Rabbi Joseph Soloveitchik called this a covenant of fate, brit goral. It  lies at the heart of Jewish identity to this day. There are Jews who  believe and those who don’t. There are Jews who practise and those who don’t. But there are few Jews indeed who, when their people are suffering, can walk away saying, This has nothing to do with me.
Maimonides, who defines this as “separating yourself from the community” (poresh mi-darkhei ha-tsibbur, Hilkhot Teshuva 3:11), says that it is one of the sins for which you are denied a share in the  world to come. This is what the Hagaddah means when it says of the  wicked son that “because he excludes himself from the collective, he denies a fundamental principle of faith.” What fundamental principle of faith? Faith in the collective fate and destiny of the Jewish people.
Who am I? asked Moses, but in his heart he knew the answer. I am not Moses the Egyptian or Moses the Midianite. When I see my people suffer I am, and cannot be other than, Moses the Jew. And if that
imposes responsibilities on me, then I must shoulder them. For I am who I am because my people are who they are.
That is Jewish identity, then and now.

Rabbi Lord Jonathan Sacks
(via yidquotes)