Eknath Easwaran's Commentary
In Hinduism and Buddhism this principle is called the law of karma. The word karma has been much misunderstood, but its literal meaning is simply action, something done. So instead of using exotic language, we might as well refer to the “law of action,” which states that everything we do – even everything we think, since our thoughts condition our behavior – has consequences: not “equal and opposite” as in physics, but equal and alike.
The comparison with physics is deliberate, for this is not a doctrine of any particular religion. It is a law of life, which no one has stated more clearly than Saint Paul: “Whatsoever we sow, that shall we also reap.” The working of this law, we should bear in mind, is not necessarily negative. If we sow mercy, we shall receive mercy in ample harvest. If we give love, we shall receive love; if we are kind and patient to others, others will be kind and patient to us.