Galileo, in a 1613 letter to his protégé Benedetto Castelli, which in 1615 he expanded into a letter addressed to Grand Duchess Christina of Tuscany, advocated for Copernicanism, refuted theological arguments against it, and defended himself against charges of heresy. In the expanded letter, Galileo asserted outright his view that “the sun [is] situated motionless in the center of the revolution of the celestial orbs while the earth revolves about the sun”. Himself a Catholic, Galileo argued that his critics in the clergy had misconstrued the relationship between holy scripture and the physical world. He agreed that “the holy Bible can never speak untruth—whenever its true meaning is understood”. But he argued that its meaning “is often very abstruse, and may say things which are quite different from what its bare words signify”. Galileo, in making this argument, sought to establish that it was his critics’ interpretation of the Bible that contradicted Copernicanism, not the Bible itself. Galileo held that the Bible was written in metaphors, to teach humans how to live. He even pointed out that literal interpretations of certain Biblical passages (e.g., those attributing to God emotions such as jealousy, anger, or hatred) would themselves constitute heresies. Galileo noted that, although “the holy Bible and the phenomena of nature” both “proceed alike from the divine Word” and thus “cannot contradict each other”, the physical world, unlike the holy Bible, “never transgresses the laws imposed upon her, or cares a whit whether her abstruse…methods of operation are understandable to men”. He argued that humanity should not use its interpretations of scripture to criticize its knowledge of physics. On the contrary, humanity should use its knowledge of physics “as the most appropriate aid in the true exposition of the Bible”. Galileo thus defended his piety while simultaneously offering an argument that not only refuted the basis for his critics’ attacks, but also proposed a powerful framework for his critics to use in correcting what were, from his perspective, their false interpretations of “the holy Bible”.