If you have a meditation practice of any kind, at some point you may want to try a variation known as tonglen, sometimes known as "taking and sending" meditation. Although I believe it originated in Tibetan Buddhist practice, the exercise isn't a religious ritual of any kind, so I think it's not likely to trouble anyone, even Christians.
Tonglen, like most forms of meditation, is a breath-based practice, and its essence is very simple: On inhalations, you visualize that you are taking in the pain and suffering of other people; and on exhalations, you are giving away your goodness to the world—offering up any and all pleasant feeling and good will you can find within you.
When I first started the practice, I was surprised to find how much resistance I had to it. Though I imagined myself to be a more or less compassionate person, there was a silent resentment to the notion of giving away my goodness and breathing in the pain and suffering of others. I began to see how conditioned I was (perhaps how conditioned we all are) to defend ourselves against pain and suffering, and to collect and hold whatever kind of pleasantness we can find in life.
Tonglen offers a way to test out what it might be like to drop that habitual defensiveness and territoriality. The results are best experienced when the practice no longer seems symbolic, but when you adopt it quite literally. You genuinely do feel that you are giving away all that is good and pleasant within you, and that you are absorbing very real pain of others. On every outbreath, you take a leap of faith and offer every last ounce of happiness you have, with no expectation of return.
If you can take the leap and practice this way in a very literal fashion, a pretty stunning realization soon sets in. No matter how much goodness you give away, more reappears instantly to replace it. It isn't a limited resource at all, but one that flows freely if you simply unclog the pipes. Even at a moment of deep despair or depression, you can, on every exhalation, always find some goodness to be handing off to others. In fact, times of low spirit are the best time to practice tonglen. And rather than feeling depleted by the suffering of other people entering you, it begins to feel like a form of nourishment. The pain you inhale is the fuel that is transformed into the peace you breathe back out. It is like the carbon dioxide inhaled by plants that they may exhale oxygen.
Your assumptions pretty soon get turned entirely upside down, for you recognize that there was never any reason to defend yourself, nor any reason to hoard goodness in any way. Rather than living in a miserly way, counting pennies, you can freely walk, because the ground is pretty well covered in gold coins. Rather than living from a perspective of poverty and deficit, we start to feel free .
Like many such practices from my adopted tradition, tonglen isn't so much a moral practice as a practical one. This is one aspect that seems quite alien to people who come from a Christian/Muslim/Judaic tradition. Giving away goodness isn't a sacrifice we make in order to be deserving of goodness in return. We do it because the tangible evidence shows that softening the ego and reversing our habits makes us feel happier in a genuine way.
Unlike some Western traditions, which are based on a kind of economic model in which we must "buy" our happiness or salvation through good deeds, in this tradition we just follow the evidence. Living in openness just plain feels better, and that's the only reason we need. It's not a matter of living in a manner that pleases some higher power into rewarding us. We live this way because it works, here and now.