In plain words
Next, man as beast. ‘Jñānena śūnyaḥ paśubhissamānaḥ’. What is bestiality? To take sense experience itself as the aim of life and sense enjoyment itself as the supreme goal of one's life, to go on enjoying the pleasures of the senses alone from birth until death, to pass one's life in food, sleep, fear and mating, and in a life of this kind to forget one's very humanness. Food, sleep, fear and mating are just the same for man and beast. What is the difference between beast and man? Only when enquiry into what lasts and what passes is wanting does he become equal to a beast. When does he not make this enquiry into what lasts and what passes? Only a man who has filled his heart with selfishness and self-interest does not take up this enquiry into what lasts and what passes. Bestiality is to be a man and give one's life over to beastly qualities and beastly conduct alone. For man to attain the highest divinity is the right and noblest path. When it is not possible to attain that divinity, for man to attain humanness and make his life worthwhile: this is one Dharma. But for man to turn into a demon and a beast: this is a Dharma gravely perverted.
Because actions of this kind have spread through the world today, humanness itself is sinking out of sight. Morality and honesty are vanishing. The norms of society have been rooted out even more. In a state where he cannot understand what society is, he is wasting his life. He thinks society is merely a gathering of heads. No. No. Society is what … the unity in the many. For all to come together, do one karma at one time, regard the fruit of that karma as of the one Ātma, and all enjoy it together: this alone is the chief duty of society. To recognise the truth that man's true happiness can be enjoyed only through it: this alone is the inner meaning of society. Without society he himself does not exist. All his happiness and joy rest on society alone. Only one who cannot recognise this truth labours for his own selfishness and self-interest.
The Taittirīya Upaniṣad has explained well the measures of these pañcāgnis and the four classes of men.