A saying from the Bible's story of Cain and Abel. After Cain had murdered his brother Abel, God asked him where his brother was. Cain answered, “I know not; am I my brother's keeper?”
Cain's words have come to symbolize people's unwillingness to accept responsibility for the welfare of their fellows — their “brothers” in the extended sense of the term. The tradition of Judaism and Christianity is that people do have this responsibility.
