(BHAGAVATA)

Sometimes, when the created world has to be sustained, I myself assume name and form and initiate Manvantharas (great eras of time) and provide the Earth with appropriate Divine Personalities and Sages, who set examples to be followed and indicate the path of progress.

I end also the unlimited increase of beings, when it happens. For this sake, I take on the form of Rudra (the destructive aspect of God). I create the bad, in order to high-light and promote the good; and in order to protect the good, I set certain limits, both to the good and the bad, for, they would otherwise, stray into wrong ways and inflict great harm.