And, since, in every thing here below, we see the resultant of two opposing forces, under him were two coequal and coeternal principles, represented by the imagery of Light and Darkness.
These principles are in never-ending conflict.

The world is their battle-ground, man is their prize.
In the old legends of Dualism, the Evil Spirit was said to have sent a serpent to ruin the paradise which the Good Spirit had made.

These legends became known to the Jews during their Babylonian captivity.
The existence of a principle of evil is the necessary incident of the existence of a principle of good, as a shadow is the necessary incident of the presence of light.

In this manner could be explained the occurrence of evil in a world, the maker and ruler of which is supremely good.

Each of the personified principles of light and darkness, Ormuzd and Ahriman, had his subordinate angels, his counselors, his armies.