"A Jew is a Jew is a Jew.

  The Marranos were enmeshed in some of the same identity-metaphysics as were their persecutors. For them, too, there was an inviolable fact of the matter concerning true Jewish identity that remained untouched by all outer performance. They may have gone through formal Christian conversions, taken the sacrament, and gone every week to confession, but within the confessional of their inner being they, too, continued to insist on their essential Jewishness.

A Sephardic friend tells me his grandfather used to tell him a joke that perhaps goes back to Marrano times. A Jew has undergone a conversion process, in the course of which the priest has put his hands on the Jew’s head and repeated several times, “You were a Jew, now you’re Christian, you were a Jew, now you’re Christian.” A few weeks pass and the priest comes on a Friday to see how his converso is getting on. The priest finds, to his shock and dismay, that the New Christian is not eating fish for his Friday night dinner, as he ought to as a good Catholic, but rather a roasted chicken. The Jew, ordered to account for himself, explains that he had simply put his hand on the chicken’s head and repeated several times, “You were a chicken, now you’re fish, you were a chicken, now you’re fish.

Rebecca Goldstein, Betraying Spinoza:The Renegade Jew Who Gave Us Modernity, p.127.