The theory of karma should not be confused with so-called "moral
justice" or "reward and punishment." The idea of moral justice, or
reward and punishment, arises out of the conception of a supreme being,
a God, who sits in judgment, who is a law-giver and who decides what is
right and wrong. The term "justice" is ambiguous and dangerous, and in
its name more harm than good is done to humanity. The theory of karma is
the theory of cause and effect, of action and reaction; it is a natural
law, which has nothing to do with the idea of justice or reward and
punishment. Every volitional action produces its effects or results. If
a good action produces good effects and a bad action bad effects, it is
not justice, or reward, or punishment meted out by anybody or any power
sitting in judgment on your action, but this is in virtue of its own
nature, its own law. This is not difficult to understand. But what is
difficult is that, according to the karma theory, the effects of a
volitional action may continue to manifest themselves even in a life
after death.
--Walpola Rahula in /What the Buddha Taught/
from /Everyday Mind,/ edited by Jean Smith, a /Tricycle/ book