When the demoniac give too much trouble to the brahmanas and the cows, Krsna descends to reestablish religious principles

TQK 26            Enchantment by Krsna' s Glories  
Why is cow protection so much advocated? Because the cow is the most important animal. There is no injunction that one should not eat the flesh of tigers or other such animals. In the Vedic culture those who are meat-eaters are recommended to eat the flesh of goats, dogs, hogs, or other lower animals, but never the flesh of cows, the most important animals. While living, the cows give important service by giving milk, and even after death they give service by making available their skin, hooves, and horns, which may be used in many ways. Nonetheless, the present human society is so ungrateful that they needlessly kill these innocent cows. Therefore Krsna comes to punish them.
   Krsna is worshiped with this prayer:

                      namo brahmanya-devaya
                      go-brahmana-hitaya ca
                      jagad-dhitaya krsnaya
                       govindaya namo namah

   "My Lord, You are the well-wisher of the cows and the brahmanas, and You are the well-wisher of the entire human society and world."For perfect human society there must be protection of go-dvija--the cows and the brahmanas. The word dvija refers to the brahmana, or one who knows Brahman (God). When the demoniac give too much trouble to the brahmanas and the cows, Krsna descends to reestablish religious principles.