On Christian Doctrine is a theological text written by Augustine of Hippo. It consists of four books that describe how to interpret and teach the Scriptures. By writing this text, Augustine set three tasks for Christian teachers and preachers: to discover the truth in the contents of the Scriptures, to teach the truth from the Scriptures, and to defend scriptural truth when it was attacked. Book One discusses enjoyment, use, interpretation, and the relation of various Christian doctrines to these concepts; Book Two discusses the types of unknown signs present in the world and defines each and presents methods for understanding the Scriptures; Book Three discusses how to interpret ambiguous literal and ambiguous figurative signs. Ambiguous signs are those whose meaning is unclear or confused; Book Four discusses the relationship between Christian truth and rhetoric, the importance of eloquence, and the role of the preacher.