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Whenever there is decline of righteousness, O Arjuna, and rise of unrighteousness, then I manifest Myself.

Whenever dharma declines, Bharata, and adharma rises up, then I bring myself forth.

This is one of the best-known verses of the Gita. Krishna says that whenever dharma weakens and adharma, disorder and wrongdoing, gains ground, he manifests himself. The idea of the avatāra, the divine descent into the world, finds its classic statement here. The verse explains why the eternal and unborn would take birth at all: to restore balance when the moral order is threatened. It also connects Krishna's presence on this battlefield to the larger purpose of upholding dharma in the world.