It is a law of mechanics that action and reaction are equal and opposite.

In the almost infinitely finer matter of the higher worlds the reaction is by no means always instantaneous; it may sometimes be spread over long periods of time, but it returns inevitably and exactly.
Just as certain in its working as the mechanical law in the physical world is the higher law, according to which the man who sends out a good thought or does a good action receives good in return, while the man who sends out an evil thought or does an evil action, receives evil in return with equal accuracy--once more, not in the least a reward or punishment administered by some external will, but simply as the definite and mechanical result of his own activity.

Man has learnt to appreciate a mechanical result in the physical world, because the reaction is usually almost immediate and can be seen by him.

He does not invariably understand the reaction in the higher worlds because that takes a wider sweep, and often returns not in this physical life, but in some future one.
The action of this law affords the explanation of a number of the problems of ordinary life.

It accounts for the different destinies imposed upon people, and also for the differences in the people themselves.