Some years after his vindication of Talmudical Judaism against the Hamburg sceptic he composed the best work (1624) that issued from his active pen. On the one side it was a weighty attack on Rabbinical Judaism, such as had hardly been made even by Christians and Karaites, on the other side, an impressive defense of it. He did not venture to put his own name to the heavy charges against Judaism, but used a fictitious name. The part which contains the attacks he called "The Fool's Voice" (Kol Sachal), and the defense, "The Roaring of the Lion" (Shaagath Aryeh). Leo Modena allotted to two characters his own duplex nature, his varying convictions. He makes the opponent of Judaism express himself with a boldness such as Uriel da Costa might have envied. Not only did he undermine the Rabbinical Judaism of the Talmud, but also biblical Judaism, the Sinaitic revelation, and the Torah. But the blows which Leo Modena, under the name of Ibn-Raz of Alkala, in an attack of unbelief, inflicted on oral teaching, or Talmudical Judaism, were most telling. He premises that no form of religion maintains itself in its original state and purity according to the views of its founder. Judaism, also, although the lawgiver expressly warned his followers against adding anything, had many additions thrust upon it. Interpretation and comment had altered many things in it. Ibn-Raz (or Leo Modena in his unbelieving mood) examines with a critical eye Jacob Asheri's code, and at each point marks the additions made by the rabbis to the original code, and where they had weakened and distorted it. He goes so far as to make proposals how to clear Judaism of excrescences, in order to restore genuine, ancient, biblical, spiritual Judaism. This was the first attempt at reform: a simplification of the prayers and synagogue service, abolition of rites, omission of the second day of the festivals, relaxation of Sabbath, festival, Passover, and even Day of Atonement laws. Every one was to fast only according to his bodily and spiritual powers. He wished to see the ritual for slaughtering animals and the laws as to food set aside, or simplified. The prohibition to drink wine with those of other creeds made Jews ridiculous, as also did the strictness against alleged idolatry. All this, observed Ibn-Raz, or Leo Modena, at the close, does not exhaust the subject; it is only a specimen of the evil of Rabbinical Judaism. He knew well that he would be pronounced a heretic, and persecuted on account of his frank criticism, but if he could open the eyes of a single reader, he would consider himself amply rewarded.