Augustine turns his attention to the topic of signs in scripture and reflects again on the power of the written word. He explains that, due to the ambiguity and symbolism in many passages of scripture, it is easy for uninformed or inexperienced readers to be led astray in their interpretations. Augustine claims that these interpretive difficulties were divinely ordained to humble the human intellect and to keep people actively engaged with the sacred texts.

In terms of the scriptural canon—that is to say, the books of scripture accepted by the Catholic Church as forming the true Bible—Augustine urges his readers to accept the authority of the most established churches on such matters. He then explains that it is important for any serious student of the Bible to learn three languages: Latin, Greek, and Hebrew. Hebrew is the language of the Old Testament, Greek is the language of the New Testament, and Latin translations of these biblical texts are numerous and (as Augustine acknowledges) can sometimes vary. Augustine tells his readers that knowing all three languages can make interpreting signs and figurative passages easier, since the learned reader can consult multiple versions of the same text.

Augustine denounces the existence and influence of pagan religions by condemning superstitions such as augury (trying to determine the future through animal sacrifices and other signs) and astrology.