Book Four discusses the relationship between Christian truth and rhetoric, the importance of eloquence, and the role of the preacher. This book was appended to the work a number of years after its original composition, along with the end of Book Three. Augustine again stresses the importance of both discovery and teaching for the interpretation of Scripture. He cautions the reader that he will not discuss the rules of rhetoric here; for though they are acceptable and useful for the Christian speaker, they can easily be learned elsewhere. Though eloquence is a skill which can be used for good or evil, it should be used in service to wisdom. It is not necessary, then, for the preacher to be eloquent, but only wise. Nonetheless, eloquence can enhance one's ability to teach wisdom. The proper goal of rhetoric should thus be to teach wisdom by the use of eloquence.