In his commentary to Sefer Yechezkel (18:6), Radak writes that once a Jew, always a Jew. “There is a covenant between Hashem and Klal Yisrael, stating that those who are descendants of Avraham, Yitzchak and Yaakov (who are of the Patriarchal lineage) will never cease their commitment to Judaism. Those, however, who, over time, apostatized themselves and reneged on their faith in Hashem had never been real descendants of the Patriarchs. They are the offspring of the asafsuf, those insincere individuals who attached themselves to the Jewish People.”
In his Igeres Teiman, the Rambam makes a similar statement: “Those who stood at Har Sinai, experiencing the Revelation, will always believe in the prophecy of Moshe Rabbeinu. This applies to them, their children and their children’s children, forever. For Hashem said to Moshe, ‘And they will forever believe in you.’ Therefore, one should know that anyone who turns away from the religion that was established at this gathering (the Revelation) is not a descendant of theirs.” In other words, Rambam reiterates that one who eschews Judaism, who turns his back on Hashem, who becomes an apostate, is not mi’zera Avraham, Yitzchak, and Yaakov. He neither descended from the Patriarchal lineage, nor did his ancestors stand at Har Sinai.
The question is now quite obvious: What about Korach? He certainly did not descend from a newcomer to the Jewish faith. No one can dispute his illustrious lineage. Nonetheless, he disputed Moshe’s leadership, claiming that Hashem did not choose him. Can there be any greater – more blatant – display of heresy than this? This question was posed to the Gerrer Rebbe, the Imrei Emes, zl, by his son-in-law.
The Rebbe replied that, indeed, Korach knew and believed in Hashem. He was, however, one who is considered a prime example of: yodea es Boro u’miskaven limrod Bo, “He knows and acknowledges his Creator, yet maliciously intends to rebel against Him.” This is a new dimension in kefirah, heresy. One knows what he is doing. He is aware and believes in Hashem, but this does not affect him. He could care less. He will rebel against his Creator because he wants to! Korach sought kavod, glory. As long as Moshe stood at the helm of Jewish leadership, Korach was relegated to a secondary position. This was something this despot could not live with – even if it meant mutinying against the Almighty.
The Steipler Gaon, Horav Yisrael Yaakov Kanievsky, zl, gives a different answer to this question. The Rambam’s position that once a Jew, always a Jew (and a Jew that reneges his Judaism had never actually been a Jew by birth lineage) applies only when nothing is in his way, nothing to distort his belief, nothing to undermine his conviction. He, of his own volition, took a philosophical approach to Judaism. In accordance with his way of thinking, he feels that the religion is unjustifiable, and, therefore, he rejects it. He did not see the miracles and wonders which are recorded in the Torah. If he did not see it, and if he cannot understand it, then he does not believe it. Such a person is not one of us – period. A Jew, however, who has sinned and fallen under the malignant spell of the yetzer hora, evil-inclination, and is thus led to heresy is nothing more than a Jewish sinner. He is one of us – a sorry case – but one of us nonetheless.
This was Korach. He could not deal with his envy. His jealousy over Moshe’s position of leadership destroyed him, making him act in the reprehensible manner that he did. Korach was a Jewish renegade – but a Jew nonetheless.