In 1715 the Reverendo, e Doutissimo Haham Asalem Morenu David Netto (ר' דוד בן פנחס ניטו) published a booklet called אש דת directed against the Sabbatean missionary Nechemia Chiya Chayon (or Hayon; Hayyun, etc.). Chayon's theology was radically antinomian; he preached the abolition of the rites and commandments of Judaism, in fulfillment of his theology of sin (sinning would elevate the sparks of holiness and bring about the Messianic redemption). In addition, he advocated a kind of Trinity, which was naturally seen as totally derivative of Christianity, not to mention idolatrous.
This was a work of scholarship, hence it was written in Hebrew. However, Nieto also wished to reach his less learned congregants, so he published a version in Spanish called Es dat, ò, Fuego legal. The Spanish version contained a preface not included in the Hebrew. At the end of the preface he indicated that he had written a Spanish supplement which could be read by anyone who is interested: “Much more could I say of the pernicious consequences of this schism, but I omit it for very strong reasons; but not to deprive my people of what affects it so much, I reserve it in manuscript in my possession, and I offer it with affectionate interest to anyone who would like to read it or to translate it” (tran. by Israel Solomons). In other words, the supplement was meant for internal communal consumption, unlike a published book which could be bought and read by anyone.
The first historian to describe the supplement was the first one to locate it: Israel Solomons had located three existing manuscripts of the supplement, which he mentioned in his 1915 JHSE paper David Nieto and Some of His Contemporaries (published in volume 12 1928-31). He had bought one copy at an auction in 1912, another was in the Bodleian Library, and a third was in New York, having been bought by Richard Gottheil in Amsterdam at an auction in 1897.
In 1981 Raphael Loewe published the entire text in an article called 'The Spanish Supplement to Nieto's 'Esh Dath,' in PAAJR 48. The supplement, called Reflexiones Thelogicas Politicas, y Morales sobre el Execrable Systema de Nehemy'a Hiya' Hayon is divided into 14 sections.
Nieto tried to argue against Chayon's theology on several grounds, one of which is that the precarious situation of Europe's Jews absolutely required that they be totally law-abiding, including especially to their own religion. He was not incorrect in the notion that the European governments did not wish to see libertine Jews. Nieto argued that the Jewish presence in Europe was acknowledged on the premise that the Jews were living by a legal and moral code. Should Jews follow Chayon and permit that which is illegal, once this became known, what would become of the Jews? Nieto - writing for Jews, remember - reminds them of what money-lending led to in the Middle Ages: ""no se amotinaran contra nos como hizieron por los exorbitantes usuras que tomovamos dellos en Espana, Francia, Ynglaterra, Alemania e Ytalia. - Will not non-Jews be incited to antipathy against us, just as they were by the exorbitant interest which we exacted from them in Spain, France, England, Germany and Italy?" This is nothing short of amazing. The usual, not entirely incorrect, line is that Jews were driven to usury by being forbidden from other kinds of work. In fact one reason Jews were readmitted to England is because Rabbi Menasseh ben Israel tried that on Oliver Cromwell scarcely 60 years earlier - and it worked. Here Rabbi Nieto speaks to Jews and does not tell them that the persecution and expulsions came out of nowhere without provocation.
Nieto knew that in 1715 European Jews could only exist through delicate balance. The oath of a Jew, for example, was accepted in non-Jewish courts on the assumption that when a Jew swore on his Bible he meant it as seriously as a Christian swearing on his. Nieto thus argued that Chayon had to be repudiated on the grounds that acceptance of his doctrine would make Jews unfit to be a part of European civil society. He writes (Loewe's translation): "What, then, would [Christians] do to us should it come to their knowledge that we do not scruple to cheat them, and that we regard such conduct as not merely legally admissible but indeed obligatory and progitable? What opinion would they form of our character, promises and conscience? What profanation of God's name!"
(Loewe points out that Nieto does not mention the extremely degrading ceremony accompanying the oath more judaico which Jews were required to take in the German states and elsewhere.)
Below is the 11th section which is a very interesting acknowledgment of European attainments in scholarship, Hebrew and other kinds of linguistic accomplishments. Nieto argues that there is no such thing as an internal Hebrew conversation:
Loewe's translation is: "It is useless to pretend to ourselves that Hayon's book, being written in Hebrew, will not come to the notice of Christians. The nations of Europe are the most intellectually powerful in the world: no science, no art eludes them, no information conceals itself from them whatever the language or script in which it is written, no matter how ancient or abtruse."
Nieto then notes Latin translations of the Kuzari, the Guide for the Perplexed, the Kabbalah Denudata (see here), which includes translations of many Zoharic passages, as well as teachings of the Ari (whom he calls Rab Asquenazy). In addition, [parts of] the Mishneh Torah of Maimonides, the complete Mishnah, and several Talmudic tractates are available in Latin. [What's more] the translations are faithful to the original (ie, accurate) having compared them himself.