The Christians, during the night before Easter (Vigils), perpetrate shameful abominations in the churches at Jerusalem, abandon themselves to debauchery, harbor thieves and murderers, and carry on bloody feuds within their precincts. They dishonor their character in the same way as the Jews profaned their Temple. Therefore, God, in His wisdom, has deprived the Jews and the Christians of the Holy City, and has intrusted it to the Mahometans, because, in their hands, it is safe from desecration. To his observation the Christian priest and the Jewish physician could oppose only abashed silence. Chayim Ibn-Musa devoted himself to the task of discrediting the chief sources of the materials of Christian attacks on Judaism, the writings of the Franciscan Nicholas de Lyra. He not only refuted the assertions put forward in those works, but deprived them of the soil upon which they fed. The ever-recurring controversies between Jews and Christians led to no conclusions, and left each party in the belief that it had gained a victory, because they generally turned on secondary questions, the disputants never discussing fundamental premises, but wrangling, each from his undemonstrated basis. Chayim Ibn-Musa wished to introduce method into these controversies, and to lay down clear principles for the defense of Judaism. Accordingly, he drew up rules which, strictly observed, were bound to lead to a definite result. In the first place, he advised Jews invariably to hold fast in a disputation to the simple meaning of the Scriptures, always to take the context into account, and especially to avoid allegorical or symbolical methods of interpretation, which left Christian polemics free to introduce arbitrary theories. Further, Jewish disputants were to announce that they ascribed no authority in matters of belief either to the Chaldaic translation of the Bible (Targum) or to the Greek (Septuagint), these being the sources of the false proofs adduced by Christians. He counseled them to abandon even Agadic exegesis, and not to hesitate to declare that it had no weight in determining the doctrines of Judaism. These and similar rules Chayim Ibn-Musa applied to the writings of Nicholas de Lyra, successfully refuting them from beginning to end in a comprehensive work, justly entitled "Shield and Sword."