"Now, mother, your cow is your mother. You drink milk of cow. And the bull is your father. Because without bull, without the cow and bull being united, there is no milk. So how is that you are eating your father and mother? It is a great challenge.
Actually those who are meat-eater, beef-eater, they are killing their father and mother and become implicated in sinful life. Therefore we say no meat-eating. No meat-eating. If you become implicated in sinful life, how you can be happy? There must be nature's punishment. Just like if you infect some disease, nature must punish you. You must suffer from the disease. You cannot get out. It is not possible. Kāraṇaṁ guṇa-saṅgo 'sya (BG 13.22). Why there are so many varieties of life? Why not one class of men, all President Nixon? (laughter) Why not? Why there is bum in the Bowery Street? In your country I am saying. Why there are arrangement of first-class, second-class, third-class, fourth-class, fifth-class men? Or animals, or trees? Everything is there. Why?
That is explained in the Bhagavad-gītā: kāraṇaṁ guṇa-saṅgo 'sya. As you have infected yourself with a particular type of modes of nature, you will get a body. That's all. If you have infected to get the body of a dog, you must be infected. People who are keeping dog, that means he is being infected by the germs of dog. Next life he will become a dog. He is infected. What he will think at the time of death? If he has got a beloved dog, he will think of... Somebody... In your country, they bequeath great, I mean to say, wealth, for the dog. That means at the time of death, at the time of death he is thinking of his beloved dog. So he must be a dog. So all his wealth goes to the dog and he goes to become a dog.
This science is unknown to the rascals. Yaṁ yaṁ vāpi smaran bhāvaṁ tyajaty ante kalevaram (BG 8.6). At the time of death, your position of the mind will create the next body. This is the science. So if you create your the position of the mind, Kṛṣṇa conscious, then you will get a body like Kṛṣṇa, sac-cid-ānanda-vigraha. This is Kṛṣṇa consciousness movement, that 'Why you shall love dog and cats? Love God, Kṛṣṇa, and you get the next body like a Kṛṣṇa.' Sac-cid-ānanda-vigraha. Anādir ādir govindaḥ sarva-kāraṇa-kāraṇam (Bs. 5.1). This is Kṛṣṇa consciousness movement, how to think of Kṛṣṇa at the time of death. Then your life is successful."
(Srila Prabhupada Lecture, Los Angeles, December 31, 1973)