3 Defend the poor and fatherless;
Do justice to the afflicted and needy.
4 Deliver the poor and needy;
Free them from the hand of the wicked.
Psalm 82:3-4. The Bible (both the Old and New Testament) is full of this type of admonishment. This is neither the time nor space to fully expound on that topic. But if you doubt that Jews and Christians are called to live in this way -- whether they've done successfully is a different matter -- you do not have a good grasp of the Judeo-Christian morality.
What I hope most honest Christians would tell you is that to care for others isn't simply a nice thing to do. It's a commandment. In fact, in its most general form that is the "greatest" of all commandments:
"Teacher, which is the greatest commandment in the Law?" 37Jesus replied: " 'Love the Lord your God with all your heart and with all your soul and with all your mind.' 38This is the first and greatest commandment. 39And the second is like it: 'Love your neighbor as yourself.' All the Law and the Prophets hang on these two commandments."Matthew 22:36-40.
One of many points of debate between observant Jews and Christians and atheistic secular humanists is the role that altruism plays in the world or, more to the point, how it got here in the first place. Christians would typically say that good put care and concern for our fellow man at the core of our being. It comes from above and did not evolve accidentally.
Humanists, looking at it from a scientific point of view, point to altruistic traits in various animals species as evidence that it can (and did) evolve through natural selection. That, of course, is something of an oversimplification of the position, but you get the point. Ultimately, atheists would say altruism, like everything else, really exists by accident. Google "altruistic bees" for more sophisticated discussions on this point.
I'm not a man of science. I know enough only to be dangerous (probably more to myself than others.) But I do grasp that evolutionistic altruism would tend to violate the principle of natural selection. A lot of scientists agree and say, for that reason, that what we see in nature is "pseudoaltruism," acts that appear to benefit others at the expense of the actor, but which ultimately benefit the actor.
To me that is all highly fascinating but, as far as human beings go, it's beside the point. If you believe a revealed, personal God exists, like the God of the Bible, you might find that altruism is something external or, perhaps, that it is a command. You might believe -- and your belief would square with the Bible -- that we should act to benefit others, even at great personal cost, and even if we do not want to do so.
The atheist has no such conviction, or at least need not have one. In the natural world, caring for the poor and infirmed is actually detrimental to a species because it either maintains an organism that should die, thus diverting resources away from healthy ones that will be replenishing the gene pool, or it causes weak organisms to create (weak) offspring. I am reminded of this by my wife when tending to the plants and flowers. She has reminded me a number of times to cut away dead flowers, leaves and stems so that resources can be divided to the healthier parts of the plant.
Of course we humans would never be so animalistic to apply that kind of thinking to human relations. We'd never starve or kill the sick, bedwetters, homosexuals, mentally disabled, Jews, or any other "undesirables." We'd never think of sterilizing humans to protect the gene pool.
Back to the point. Christians -- honest ones -- have to care for their fellow man whether they want to or not. All kinds of good, kind-hearted atheists or non-believers of other stripes might (and certainly often do) care for people, but they don't have to. Without an external moral compass, one that supersedes their own personal will or longings or desires, they would be right, based on their own view of nature, to disregard the needs of everyone else but themselves. That they often don't follow what they believe to be the way of nature suggests that they are bathed in the light of Christian morality, whether they like it or not.