CHAPTER I. The Occasion and Purpose of this "Manual"
1. I cannot say, my dearest son Laurence, how much your learning pleases me, and how much I desire that you should be wise-though not one of those of whom it is said: "Where is the wise? Where is the scribe? Where is the disputant of this world? Hath not God made foolish the wisdom of this world?"  Rather, you should be one of those of whom it is written, "The multitude of the wise is the health of the world"  ; and also you should be the kind of man the apostle wishes those men to be to whom he said,  "I would have you be wise in goodness and simple in evil." 
2. Human wisdom consists in piety. This you have in the book of the saintly Job, for there he writes that Wisdom herself said to man, "Behold, piety is wisdom."  If, then, you ask what kind of piety she was speaking of, you will find it more distinctly designated by the Greek term theosebeia, literally, "the service of God." The Greek has still another word for "piety," ensebeia, which also signifies "proper service." This too refers chiefly to the service of God. But no term is better than theosebeia, which clearly expresses the idea of the man's service of God as the source of human wisdom.
When you ask me to be brief, you do not expect me to speak of great issues in a few sentences, do you? Is not this rather what you desire: a brief summary or a short treatise on the proper mode of worshipping [serving] God?
3. If I should answer, "God should be worshipped in faith, hope, love," you would doubtless reply that this was shorter than you wished, and might then beg for a brief explication of what each of these three means: What should be believed, what should be hoped for, and what should be loved? If I should answer these questions, you would then have everything you asked for in your letter. If you have kept a copy of it, you can easily refer to it. If not, recall your questions as I discuss them.
4. It is your desire, as you wrote, to have from me a book, a sort of enchiridion,  as it might be called-something to have "at hand"-that deals with your questions. What is to be sought after above all else? What, in view of the divers heresies, is to be avoided above all else? How far does reason support religion; or what happens to reason when the issues involved concern faith alone; what is the beginning and end of our endeavor? What is the most comprehensive of all explanations? What is the certain and distinctive foundation of the catholic faith? You would have the answers to all these questions if you really understood what a man should believe, what he should hope for, and what he ought to love. For these are the chief things-indeed, the only things-to seek for in religion. He who turns away from them is either a complete stranger to the name of Christ or else he is a heretic. Things that arise in sensory experience, or that are analyzed by the intellect, may be demonstrated by the reason. But in matters that pass beyond the scope of the physical senses, which we have not settled by our own understanding, and cannot-here we must believe, without hesitation, the witness of those men by whom the Scriptures (rightly called divine) were composed, men who were divinely aided in their senses and their minds to see and even to foresee the things about which they testify.
5. But, as this faith, which works by love,  begins to penetrate the soul, it tends, through the vital power of goodness, to change into sight, so that the holy and perfect in heart catch glimpses of that ineffable beauty whose full vision is our highest happiness. Here, then, surely, is the answer to your question about the beginning and the end of our endeavor. We begin in faith, we are perfected in sight.  This likewise is the most comprehensive of all explanations. As for the certain and distinctive foundation of the catholic faith, it is Christ. "For other foundation," said the apostle, "can no man lay save that which has been laid, which is Christ Jesus."  Nor should it be denied that this is the distinctive basis of the catholic faith, just because it appears that it is common to us and to certain heretics as well. For if we think carefully about the meaning of Christ, we shall see that among some of the heretics who wish to be called Christians, the name of Christ is held in honor, but the reality itself is not among them. To make all this plain would take too long-because we would then have to review all the heresies that have been, the ones that now exist, and those which could exist under the label "Christian," and we would have to show that what we have said of all is true of each of them. Such a discussion would take so many volumes as to make it seem endless. 
6. You have asked for an enchiridion, something you could carry around, not just baggage for your bookshelf. Therefore we may return to these three ways in which, as we said, God should be served: faith, hope, love. It is easy to say what one ought to believe, what to hope for, and what to love. But to defend our doctrines against the calumnies of those who think differently is a more difficult and detailed task. If one is to have this wisdom, it is not enough just to put an enchiridion in the hand. It is also necessary that a great zeal be kindled in the heart.
 I Cor. 1:20.
 Wis. 6:26 (Vulgate).
 Rom. 16:19.
 A later interpolation, not found in the best MSS., adds, "As no one can exist from himself, so also no one can be wise in himself save only as he is enlightened by Him of whom it is written, 'All wisdom is from God' [Ecclus. 1:1]."
 Job 28:28.
 A transliteration of the Greek encheiridion, literally, a handbook or manual.
 Cf. Gal. 5:6.
 Cf. I Cor. 13:10, 11.
 I Cor. 3:11.
 Already, very early in his ministry (397), Augustine had written De agone Christiano, in which he had reviewed and refuted a full score of heresies threatening the orthodox faith.