Evil exists in the world because good people are fewer, younger, weaker, less wise, and less decisive than evil people. This state of humanity might be in accord with God’s plan. There are verses in the Brhadaranyaka Upanishad which claim that Prajapati, the creator God who emanates from the supreme cosmic spirit, first created the demons, who were old, strong, and many, and then he created the Gods, who were young, weak, and few.
Here’s the translation of verse 1.3.1:
“Prajapati gave rise to two classes of descendants: the Gods and the Demons. The Demons were created first and were the elder ones, the Gods were the younger ones. The two classes struggled with each other to gain mastery of the universe. The Gods said, “Come, let us overcome the demons at the sacrifice through the Udgitha.”
The insight that I gather from this verse is that the Gods are not only younger, they are also fewer and weaker than the demons. This is a reflection of the state of humanity—the Gods (the good people) are always fewer and weaker than the demons (the bad people), and the Gods generally arrive on the scene after the demons have created great chaos, bloodshed, and destruction. The struggle between the Gods and the demons, between the good and evil, never ends, but in most conflicts, it is the demons (the bad people) who win.
The real meaning of this verse is different from what I have just said:
The Gods and the demons in this verse are the organs, speech, and the rest of Prajapati—these are inclined towards material things or spiritualism, towards good or evil. When they are inclined towards the good as preached in the scriptures, they are the Gods, and when they are inclined towards the evil and go against the teachings of the scriptures, they are the demons. The distinction between the Gods and demons is a distinction of values, not of beings.