It is the eternal nature of things existing independently of the will of the Creator or of any other being.
What is the cause of the existence of this created system? It is the will of the Creator.
What is the cause or reason why God willed that this system should be as it is, with all the evil that exists? It is because it is the best system possible in the nature of things.
What is the cause or reason that any given event, however evil, is not prevented by God? It is because any change that would prevent it, would alter the best possible system, and thus make more evil than the one thus prevented.
Chapter XXIII. Laws and Penalties—Sin and Holiness.
The laws of God, in regard to voluntary action, are those invariable arrangements in mind and matter by which happiness or pain are connected with certain feelings and actions.
Thus it is an invariable arrangement that pain shall be connected with touching fire, and pleasure with seeing the light. So in regard to the intellect; pleasure is invariably connected with the exercise of wit and humor, and disgust with folly and fatuity. So the moral sense is invariably pleased with truth, justice, and integrity, and pained by the opposite.
Whenever, therefore, we discover what invariably affords pleasure or pain, we discover one of the laws of God.
To discover these laws, and to believe in them, is as indispensable to the right action of mind as light is indispensable to perfect eyes in order to see.