This is the supreme law of balance. The Law of Karma is instigated to ultimately attain harmony, because the purpose of Karma is to obtain harmony.
In physical terms, consider the harmony of a still pond. If a person throws a stone into it, the harmony is disturbed. The person is the cause, the splash and ripples are the effect. Similarly, a persons inharmonious actions flow out into the universe, back and forth, through subsequent lifetimes, until that persons' harmony is restored.
We can attain peace when we are in harmony with the Laws of the Collective Spirit. The peace we seek is that which comes by being one in soul, mind and heart with the Collective Spirit.