Augustine wrote his book On Christian Doctrine (or better translated: On Christian Instruction) as a manual for a Christian teacher. As such, the English title may be a bit misleading, because it is not about the doctrines of the Christian faith. Rather, it is an overview of hermeneutics and homiletics (to use modern terminology).
In his first book, he discusses the life of a preacher and argues how it is necessary for him to love and enjoy God and note get entangled with this world. His second book switches to hermeneutics, were he discusses various means at determining the meaning of the text from a translation. His third book discusses various rules for understanding ambiguous metaphors and how to identify them. Book four switches to the matter of rhetoric, where he argues that a Christian should use it to communicate the truth.
Augustine begins his work with a short apology. He mentions that people may object to the rules of hermeneutics that he is laying down because the Holy Spirit teaches everything and therefore there is no need for a human to teach these things. He answers this objection by noting that just like people who know the language must be taught how to read the language, so to those who know Scripture must be taught how to read Scripture in order that they interpret it properly.
(Chpt. 1) He began his book by giving an outline for his work which (in modern terminology) is 1) hermeneutics and 2) homiletics. Because the undertaking of these two items is so great, he professed his dependence on God to accomplish it. He starts with the fundamentals of communication by differentiating between a thing and a sign. A thing is an object that refers only to itself and a sign is an object that refers to another object. He develops the idea of the thing in book one, while in books two and three he develops the idea of the sign.
(Chpts. 2-9) Within the category of things there are two subcategories: things used, and things enjoyed. Things used are objects that are used to get to a greater goal. Things enjoyed are objects that are an end in themselves and bring happiness. God is the only thing that should be enjoyed supremely. When men use the word God, they think of the greatest being possible. He is unchangeable including in His wisdom. And this unchanging wisdom is better than mankind’s unchanging wisdom. Thus, it is mankind’s duty to seek this unchanging wisdom.
(Chpts. 10-21) But man is impure and must be purified to see God. And so, God came, and Wisdom was incarnated as a man. Wisdom then healed man’s soul by dying and rising again for them. Men who believe by faith in the death and ascension are made stronger by hope and in the face of judgment will love and obey God. Wisdom then continues to purify men by using afflictions, forgiveness and the church. Thus, with a pure heart man can enjoy God who is eternal and unchangeable and a man can love his fellowman as means to enjoy God.
(Chpts. 22-26) Men ought to love good things as a means to enjoy God, such as his fellow men, angels, and even his own self. A man does not need to be commanded to enjoy himself, he does it naturally. Even if he abuses himself, he does not actually hate himself. And even if he may do something that hurts his body, he does it because he loves something more than his body. Even so, the command to love God and love people also includes one’s own self.
(Chpts. 27-35) But a man’s love for self is subservient for his love for others which is under his love for God. And since a Christian should love his fellow man, he is to do so equally to all men. But since he does not meet all men at all times, he is merely to love those which Providence arranges for him to meet. In a man’s love for others, he is to encourage the other to love God more. Further, men are to love angels also, because they are man’s neighbor. As for God, He uses man rather than enjoys man. He uses man with references to His goodness. And since God is the originator of all things, he does not gain any advantage from using man, rather man is advantaged from Him. Further, a man should only enjoy another man in God, otherwise he clings to temporal things. Christ came in the flesh to save men, but as he left the temporal things of earth, so too he desires believers to leave behind the temporal things of earth and love him more.
(Chpts. 36-40) In sum, man should love God who is a thing to be enjoyed and he should love man or angel which is a thing that shares in the same enjoyment of God. Those who teach Scripture must build up this love for God and man in his teaching. If he teaches falsehood, he will lose his faith in God for he cannot reconcile his error with other parts of Scripture. If he loses his faith in God, he will also lose his love for God and live in a world with no hope. But as he learns the Scripture rightly and grows in faith, hope, and love, then he has no need of the Scriptures any longer except to teach others.
(Chpts. 1-6) A sign is a thing which points to something else. Signs can be both natural and conventional. Natural signs unintentionally point to something else, but there is little to no deeper meaning than the sign itself. Conventional signs are created to expresses ideas between beings. Conventional signs can be pictures, gestures, flashes of light, etc. But the sign that communicates the most information is the written word. Word-signs record the sounds that are part of man’s speech. And so, Scriptures are records of the communication that the author’s intended men to hear. But there are many obscure passages of Scripture which men twist. These obscure passages exist, however, to humble interpreters and make them toil for meaning. This meaning is found by comparing the text with other clear passages of Scripture.
(Chpts. 7-9) As for the interpreter himself, when he approaches the text, he needs to have seven attributes so that he correctly interprets: fear, piety, knowledge, resolution, counsel, purification, and wisdom. Knowledge is the most important part of correct interpretation. An interpreter must know the entire canonical Bible so that he does not fall into error. There are three rules he must follow: 1) read and nearly memorize the entire canon; 2) understand deeply the doctrines which are plain; and 3) draw on the familiar passages to interpret the obscure.
(Chpts. 10-16) The obscurity of a passage comes from two types of signs: the unknown sign and the ambiguous sign. To clarify the obscure signs, knowledge of the Biblical languages is necessary for both understanding untranslated words and comparing translations. Often, multiple good translations can capture the meaning of a passage. But one should be wary of bad translations, which should be corrected. A more word-for-word translation should be used to correct the freer versions. If the sign is an ambiguous idiom, the interpreter must inquire of its meaning from the native speakers or by comparing multiple good translations.
(Chpts.17-35) Also, the interpreter must use the heathen’s knowledge, insofar as it is good. Their knowledge falls into two categories: things instituted by men, and things instituted by God. Many of the practices instituted by men are worthless, but some are good though superfluous, and others convenient and necessary. The things instituted by God clarify meanings in scripture, such as history, science, and kinetics. The greatest use of the heathen’s knowledge is their logical systems. The interpreter must know the difference between valid logical sequences and invalid logical sequences, and how to properly infer meaning from a text. Further, the art of rhetoric should be used to convince someone of the argument expressed in Scripture. This art, however, must be kept in balance and not used to convince someone of falsehood. The final knowledge that can be used is that of numbers, which man did not create, but discovered. All this knowledge must not be used to puff up the interpreter, but rather he should humbly approach the Scriptures.