There is the feeling, nourished by an obscure, undefined, and unverifiable apprehension, that the Jews have something strange and hidden about them.
This apprehension is of course another reason for hatred of the Jew, a hatred that has no rational causes and is not the result of the presence of Jews among another people.
In fact, the opposite is true.
Jews have shown in their lives, as in their dying for their adopted homeland, an extraordinary loyalty.
But for all their sincere identification with their surrounding society, there has remained among the people of that society a sense that the Jew, by his very essence, is not “one of us.”
They feel that somewhere within the Jew there is a strangeness, a kernel that cannot be changed or eradicated.
The assumption about an unchangeable kernel of Jewishness is not necessarily a matter of prejudice or antagonism.
On the contrary, it is rooted in the self-recognition of the Jew himself, as expressed by the halachic statement, “Israel, even though it has sinned, remains Israel” (Sanhedrin 44a).
It is a basic Jewish mystical axiom (Tanya, chapters 14 and 18) that the soul of Israel cannot be completely eliminated, even when a Jewish individual chooses to suppress it and keep it totally hidden away.
–Rabbi Adin Steinsaltz
From We Jews, Chapter 1, by Rabbi Adin Steinsaltz