.In relation to them, all people are Nazis; for the animals it is an eternal Treblinka. --Isaac Bashevis Singer, "The Letter Writer"

In his thoughts, Herman spoke a eulogy for the mouse
who had shared a portion of her life with him and who,
because of him, had left this earth. "What do they
know--all these scholars, all these philosophers, all
the leaders of the world--about such as you? They have
convinced themselves that man, the worst transgressor
of all the species, is the crown of creation. All other
creatures were created merely to provide him with food,
pelts, to be tormented, exterminated. In relation to
them, all people are Nazis; for the animals it is an
eternal Treblinka.

--Isaac Bashevis Singer, "The Letter Writer"

Isaac Bashevis Singer (1902 -1991) was a Jewish American Author. Most famous for his short stories and among the most powerful of pro-animal voices of the twentieth century Isaac Singer was born in Leoncin a village near Warsaw, Poland. In 1935 as a result of the growing Nazi threat in neighbouring Germany, Singer left Poland and followed his elder  brother Joshua to the USA.

Isaac Bashevis Singer

[M]y vegetarianism is a great protest. And I dream that there may be a whole religion based on protest … against everything which is not just: about the fact that there is so much sickness, so much death, so much cruelty. My vegetarianism is my religion, and it's part of my protest against the conduct of the world.

I did not become a vegetarian for my health, I did it for the health of the chickens.Isaac Bashevis Singer

He was parted from his common law wife  Runia Pontsch and son Israel Zamir who instead went to Moscow and then Palestine, they would not meet again until 1955. Sadly his mother, younger brother, and many members of his extended family who remained in Poland were killed. In New York where Singer made his home he worked as a Journalist for the a Yiddish-language newspaper.  In 1938, he met Alma Wassermann  a German-Jewish refugee from Munich whom he married in 1940. After which time and after some initial despondence Singer became a prolific writer and one of the leading figures in the Yiddish literary movement; he received the Nobel Prize in literature in 1978.

In a Newsweek interview, 16 October 1978, after winning the Nobel Prize in literature Singer Said:

"The same questions are bothering me today as they did fifty years ago. Why is one born? Why does one suffer? In my case, the suffering of animals also makes me very sad. I'm a vegetarian, you know. When I see how little attention people pay to animals, and how easily they make peace with man being allowed to do with animals whatever he wants because he keeps a knife or a gun, it gives me a feeling of misery and sometimes anger with the Almighty. I say "Do you need your glory to be connected with so much suffering of creatures without glory, just innocent creatures who would like to pass a few year's in peace?" I feel that animals are as bewildered as we are except that they have no words for it. I would say that all life is asking: "What am I doing here?"

Singer  wrote and published in Yiddish and then edited his novels and stories for their American versions, which than became the basis for all other translations; he referred to the English version as his "second original"  His writing accomplishments include at least 18 novels, 14 children's books, however Many of his stories and novels remain unpublished. He also wrote a number of memoirs, essays and articles. His short stories appeared in over a dozen collections.  His novels include Enemies, a Love Story, which is set 1949 New York and follows the life of Holocaust survivor Herman Broder in which the famous quote appears.

As often as Herman had witnessed the slaughter of animals and fish, he always had the same thought: in their behaviour toward creatures, all men were Nazis. The smugness with which man could do with other species as he pleased exemplified the most extreme racist theories, the principle that might is right. 
Isaac Bashevis Singer, Enemies, a Love Story

Most of Singers' later novels and stories set in America are about survivors of the holocaust and it was a perspective from which he often viewed the world, most particularly concerning the exploitation and slaughter of animals which greatly distressed him. He used some of his stories and novels as a platform to expresses his opinion concerning the exploitive and abusive treatment of animals. Singer often employs first-person narrators in his fiction that are clearly meant to represent him personally as in the above quotation.

His profound sensitivities to suffering including the suffering of animals is expressed in his autobiographical book, Lost in America:

There reposed within me an ascetic who reminded me constantly of death and that other's suffered in hospitals, in prisons, or were tortured by various political sadists. Only a few years ago millions of Russian peasants starved to death just because Stalin decided to establish collectives. I could never forget the cruelties perpetrated upon God's creatures in slaughterhouses, on hunts, and in various scientific laboratories. 

Singer's writings have had a great influence by highlighting the plight of animals and human mistreatment of them.

For the last thirty-five years of his life Singer was a prominent Vegetarian, he often included such themes in his writings. For example in his short story The slaughterer  wherein he describes the anguish that a slaughterer had trying to reconcile his compassion for animals with his job of slaughtering them.

In this extract from his short story Singer tells how the killing of animals effects one man - the Slaughter. In this except the slaughterer Yoineh Meir haunted  with misgivings takes a stroll in the night

Since Yoineh Meir had begun to slaughter, his thoughts were obsessed with living creatures. He grappled with all sorts of questions. Where did flies come from? Were they born out of their mother's womb or did they hatch from eggs? If all the flies died in winter, where in the new ones come from in the summer? And the owl that nested under the synagogue  roof - what did it do when the frost came? Did it remain there? Did it fly away to warm countries? How could anything live in the burning frost, when it was scarcely possible to keep warm under the quilt?

An unfamiliar love welled up in Yoineh Meir for all that crawls and flies, breeds and swarms. Even the mouse - was it their fault that they were mice? What wrong does a mouse do? All it wants is a crumb of bread, a bit of cheese. Then why is the cat such an enemy to it?

Yoineh Meir rocked back and forth in the dark. The rabbi may be right. Man cannot and must not have more compassion than the Master of the universe. Yet he, Yoineh Meir, was sick with pity. How could one pray for life for the coming year, or for a favourable writ in Heaven, when one was for robbing others of the breath of life? 

Yoineh Meir thought that the Messiah Himself could not redeem the world as long as injustice was done to beasts. By rights everything should rise from the dead: every calf, fish, gnat, butterfly. Even in the worm that crawls in the earth there glows a divine spark. When you slaughter a creature you slaughter God...

Quoted in the The vegetarian Magazine article, The Compassionate writer by Duba Descowitz