Why should I care for people I have never met?
Why should I care for people who are not like me?
You are apart of the human race; it's just that simple. You should not think of yourself as the only one on the planet. No one would argue with you that you are not a unique individual but regardless of your sex, race, creed, color, or religious affiliation, you are NO MORE IMPORTANT than any other individual or group of individuals on this planet.
If your religious beliefs stems from one of the Abrahamic traditions (Christianity, Islam, or Judaism), it is your religious duty to look after your fellow human beings. The meaning of the story Cain and Abel, found in the book of Genesis, is that you ARE your brother's and sister's keeper. Erich Fromm summarizied this point quite nicely, "The idea expressed in the Biblical 'Love thy neighbor as thyself!' implies that respect for one's own integrity and uniqueness, love for and understanding of one's own self, cannot be separted from respect and love and understanding for another individual. The love for my own self is inseparably connected with the love for any other being" ("The Art of Loving," page 53). The Biblical expression 'Love thy neighbor as thyself!' is not conditional. Meaning, a human being does not exclude certain members from being his neighbor. Even William F. Buckley used the line "Are you not your brother's keeper?" in his criticism of the Christian Right and its ideas of welfare reform during a discussion on "Firing line."
If you are a FreeThinker (an Atheist, an Agonistic, Deist or Humanist), using Plato's account of Socrates' discussion on the nature of justice, it is your civic duty to act justly. Regardless of your religious or intellectual mind set, you should take care of your fellow human being because they take care of you. No one achieves greatness in a vacuum.