St. Augustine, the great Church Father and Bishop of Hippo, is usually remembered as a theologian, one of the most important and original thinkers in the first millennium of Christianity, and a celebrated Doctor of the Church. His contributions to ecclesiology, sacramental theology, the theology of grace and and doctrine of original sin are all of immense value. Yet Augustine was also capable of writing on matters less lofty, and one of the greatest examples of this are the thirty chapters on homiletics that appear in Book IV of his classic work De Doctrina Christiana. This article will summarize the thinking of this great Doctor on the subject of homiletics as found in Book IV of De Doctrina Christiana.
De Doctrina Christiana
De Doctrina Christiana was composed by Augustine for the purpose of instructing Christian clergy in successfully teaching the Scriptures to their congregations. The four books of De Doctrina Christiana speak of various subjects of interest to would-be biblical scholars: understanding the difference between literal and symbolic passages, which biblical translations to use, how to resolve passages from different translations that are rendered differently, how and when to integrate non-Christian disciplines into Christian preaching, and, the subject of this article, how a Christian preacher should go about composing and delivering homilies that are educational, pleasing to listen to, and capable of bearing fruit. This is the subject of Book IV, written relatively late (426 - the other three books were composed in the 390s) and occupying the last thirty chapters of the work.
Augustine begins Book IV by reflecting on the importance of homiletics. Augustine of course does not use the word "homiletics", but rather he says that a Christian preacher must find a way to be effective at "teaching what we have learned" , but he primarily means this in the context of preaching during the Mass, so we may rightly appropriate his writings here to the subject of homiletics.
Besides the evident purpose of homiletics as a means of instructing the faithful, St. Augustine begins his discussion by noting that it is especially important that the Christian pastor be able to speak the truth of the Gospel eloquently because there are so many competing philosophies and religions in the world. These are rivals to the truth, and their own adherents are often gifted with charisma and eloquence by which they manage to draw away the weak and impressionable with smooth words. Therefore, the preacher of truth needs an eloquence of his own sufficient to counter the demagogues of the world. To profess otherwise is to simply stand by and let the sheep be devoured by the wolves:
"Should they speak briefly, clearly, and plausibly while the defenders of truth speak so that they tire their listeners, make themselves difficult to understand and what they have to say dubious? Should they oppose the truth with fallacious arguments and assert falsehoods while the defenders or truth have no ability either to defend the truth or to oppose the false? Should they, urging the minds of their listeners into error, ardently exhort them, moving them by speech so that they terrify, sadden and exhilarate them, while the defenders of truth are sluggish, cold, and somnolent? Who is so foolish as to think this be wisdom?" 
In other words, why should the devil have all the good music? If the enemies of truth use their charisma, eloquence and powers of argumentation to assail the truth, the Catholic priest ought to be at least as skilled in these arts of persuasion to fend off the fiery darts of the evil one. This is how Augustine sets up his argument that the Catholic preacher should be "eloquent."
But how does one attain eloquence? In Augustine's day, it was common for orators to learn the art of public speaking at rhetorical schools, such as Augustine himself once ran prior to his conversion. There, would-be orators would study the arts of public speaking and refine their skill with the guidance of rhetorical masters. Augustine, however, denies that this sort of training is necessary for a Catholic priest and suggests that there is another way in which eloquence might be obtained: by reading the writings and listening to the speeches of other eloquent men. He says:
"Those with acute and eager minds more readily learn eloquence by reading and hearing the eloquent than by following the rules of eloquence. There is no lack of ecclesiastical literature, including that outside of the canon established in a place of secure authority, which, if read by capable men…will imbue him with that eloquence which he is studying. And he will learn eloquence especially if he gains practice by writing, dictating, or speaking what he has learned according to the rule of piety and faith." 
Augustine had studied all of the classical rules of elocution, but it was listening to the preaching of St. Ambrose that most perfectly formed in him the ideal of how a Christian bishop should preach. The way to become erudite in the Faith is not to study the rules of erudition, but to study the Masters and Fathers of the faith. This is an important point for today. Too frequently it happens that a Catholic priest is a weak homilist. Sure, he may have studied homiletics in seminary; sure, he probably was trained as a public speaker, but according to Augustine, his time would be better spent either listening to other eloquent men speak or else reading the writings of the saints and doctors, through whom the priest will be enkindled in the faith, hope and charity. The Faith has a way of bringing forth fruits and empowering the faithful, and Augustine clearly believes that it is more important to pick up the elements of good preaching from listening to eminent preachers rather than by studying the arts of preaching.
How to Put Homiletics to Use
For Augustine, the good homilist is simply he who speaks with wisdom, and Augustine says "a man speaks more or less wisely to the extent that he has become more or less proficient in the Holy Scriptures."  So homiletics is basically a manner of teaching the Scriptures, and to this day the textbook definition of a homily is an exegesis of the daily readings. But Augustine further subdivides homiletics into three purposes or ends, and the perfect homilist, the priest who truly speaks with wisdom, is able to attain all three ends in his preaching.
"He who is eloquent should speak in such a way that he teaches, delights and moves." 
Teaching, delighting and moving are the three ends of a homily. Augustine further elaborates these points and will spend a considerable amount of time in Book IV teasing out the ideas inherent in each of these concepts:
"Thus the expositor and teacher of the Divine Scripture, the defender of right faith and enemy of error, should both teach the good and extirpate the evil. ..he should conciliate those who are opposed, arouse those who are remiss, and teach those who are ignorant of his subject what is occurring and what they should expect. ..If those who hear are to be taught, exposition must be composed, if it is needed, that they may become acquainted with the subject at hand. In order that these things which are doubtful may be made certain, they must be reasoned out with the use of evidence. But if those who hear are to be moved rather than taught, so that they may not be sluggish in putting what they know into practice and so that they may fully accept those things which they acknowledge to be true, there is needed for greater powers of speaking. Here entreaties and reproofs, exhortations and rebukes, and whatever other devices are necessary to move minds must be used." 
Here we have a point that is lost in modern homiletics. Too often modern homilies are written with an aim towards only one of these ends, but seldom all three. Some "intellectual" priests preach in such a way that information is conveyed, but they are not a delight to listen to, nor are the auditors moved to amend their lives. Some of the more "happy clappy" priests tend to try to compose homilies that make the congregation laugh and are easy and pleasant to listen to, but neither communicate any real knowledge nor move the listeners to do good deeds. Missionary priests are examples of homilists that try very hard to move their listeners to charitable actions and good deeds, typically by recounting stories of how hard their life is in the third world and appealing to arguments ad miserecordiam to appeal to the listeners pity. These homilies typically have very little intellectual content and are also not very pleasing to sit through. So we have a situation in which one end is focused on, usually to the exclusion of the two others.
How rare it is to find a priest who can teach, delight and move! Yet Augustine says this should be the aim of the homilist, and when these three ends are successfully attained, the result is what St. Augustine calls a "wholesome sweetness" or a "sweet wholesomeness", for "what is better than a wholesome sweetness or a sweet wholesomeness? The more eagerly the sweetness is desired, the more readily the wholesomeness becomes profitable."  The homily has to be both wholesome and sweet for it to be profitable.
And what is a profitable homily? A homily that teaches the intellect, delights the affections and moves is profitable ultimately if it persuades. These three ends or styles of homiletics all converge in seeking to persuade the listener:
"For it is the universal office of eloquence, in any of these three styles, to speak in a manner leading to persuasion; and the end of eloquence is to persuade of that which you are speaking…if he does not persuade, he has not attained the end of eloquence." 
If something is successfully taught to another, it means another is persuaded of its intellectual veracity; if ones affections are delighted, it means we are persuaded that something is enjoyable; if we are moved to action, it means that the will is persuaded that something is a good and that it should try to attain it. In all cases, a successful homily, one that is wholesomely sweet, is one that is capable of persuading the listener.
Characteristics of a Good Homily
Having laid the groundwork that good homiletics is necessary and what the end of a good homily should be, St. Augustine goes on to consider some practical points on things to do and to avoid.
First, Augustine recommends that complicated matters should be avoided. Augustine says some theological matters are inherently complex and do not serve well as subjects for homilies:
"For there are some things which with their full implications are not understood or are hardly understood, no matter how eloquently they are spoken, or how often, or how plainly. And these things should never, or only rarely on account of some necessity, be set before a popular audience…The speaker should not consider the eloquence of his teaching but the clarity of it." 
It is a common snare of priests to try to impress their congregations by preaching on complicated theological matters; perhaps there are some who are edified by this sort of thing, but remember, a homily has to be accessible to the weakest and lowest of the flock as well as the highest, so it needs to be something the educated can find edifying but the uneducated can find sustenance in as well - in other words, it has to be as lofty and as simple as the faith itself. Some theological concepts cannot be succinctly lectured on regardless of how gifted the homilist is, and these topics ought to be generally avoided.
Similarly, a priest ought to avoid raising questions he cannot answer:
"It is relevant to teaching not only to explain those things that are hidden and to solve the difficulties of questions, but also, while these things are being done, to introduce other questions which might by chance occur, lest what is said be rendered improbable or be refuted by them. But they should be introduced in such a way that they are answered at the same time, lest we introduce something we cannot remove." 
Do not preach on subjects like the "problem of evil" or the mystery of predestination if you cannot resolves the questions you are bringing up, lest you leave the hearers doubting rather than edified. Following Augustine's suggestion that complicated matters should be avoided, those questions that are in fact raised should be quickly answered. And, once a question is answered or a point understood, the priest should either end the homily or move quickly on to the next point, lest he weary the congregation:
"As soon as it is clear that the audience has understood, the discourse should be finished or another topic should be taken up. For just as a speaker who makes clear what is to be learned is pleasing, a speaker who insists on what is already known is burdensome." 
As to the subject matter, Augustine states that the mysteries of faith and those things that tend towards eternal life are the only proper subjects for a homily:
"Among our orators, however, everything we say, especially when we speak to the people from the pulpit, must be referred, not to the temporal welfare of man, but to his eternal welfare and the avoidance of eternal punishment." 
This might seem commonsense, but it is an important point. I have heard missionary priests and liberal priests deliver long homilies directly towards the temporal welfare of man simply without any reference to eternal life. I have also heard conservative priests utilize the entire homily to attack the policies of Barack Obama or the Affordable Care Act or other political issues, similarly without reference to eternal life, or with only a casual mention of it at the very end as a means of establishing plausible deniability lest anyone accuse them of preaching pure politics. These things should not be so; "We preach Christ crucified"; these words of St. Paul ought to be our own.  Yes, evil politicians need to be exposed. Yes, temporal welfare of the poor is important. But if these subjects are going to be the subject of a homily, they need to be referred to our ultimate destiny, so that in the end we come away from the homily with a firmer bond to our Lord and salvation. We expect to hear the Word of Life preached at Mass, not politics, whether conservative or liberal. If a priest is skilled enough to let his political commentary find an integrated place with reference to eternal things, well and good, but few priests have this skill, and that being the case, it would be best to leave these discussions for another time outside of the Mass.
Regarding oratorical style, Augustine recommends that a homilist use enough "ornamentation" to engage and persuade his hearers, but not so much that his rhetoric comes off as ostentatious or showy:
"That moderate style of eloquence when used by our eloquent churchman should neither be left unornamented nor be ornamented indecently." 
The style should be sufficient to convince the hearers or impress the outsider, but not to the degree that the speaker is suspected of simply showing off his oratorical skill. In all things, charity is the rule and persuasion is the goal.
Finally, I think it goes without saying that priests ought to preach on things that encourage people to do good, not evil, but St. Augustine has a very poignant quote about this issue or priests praising iniquity that I think is relevant to our time. He prays:
"May it never happen to us that our priests applaud those speaking iniquity and that our people love such things! May this madness, I say, never happen to us, for what should we do in the end?" 
Indeed. What shall we do in the end?
As he closes his work, St. Augustine offers two final pieces of advice: pray and live the message.
Prayers should always be offered before composing any homily, remembering that it is the Holy Spirit's job to convince people of the truth, and that "Whether one is just now making ready to speak before the people or before any group or is composing something to be spoken later before the people or to be read by those who wish to do so or are able to do so, he should pray that God may place a good speech in his mouth."  I am sure most priests pray before composing a homily, but it is good to be reminded that when preaching our pastors are preaching "not...the word of men, but as it is indeed the word of God, who worketh in you that have believed." It is goo to remember that the efficacy of a priest's words comes from God, and therefore it is fitting that God be invoked.
Finally, live the message. A priest's exhortations are abundantly more effective if he himself is living the precepts of the Gospel. Augustine concludes his work by reminding us:
"[T]he life of the speaker has greater weight in determining whether he is obediently heard than any grandness of eloquence." 
There are many other things that could be said about preaching and homiletics, but these snippets of advice, taken from one of the greatest preachers in the history of Christendom, provide a good outline for how a priest ought to construct a good homily.
 St. Augustine, De Doctrina Christiana, Book IV,1:1
 ibid. IV,2:3
 ibid. IV,3:4
 ibid. IV,5:7
 ibid. IV,12:27
 ibid. IV,4:6
 ibid. IV,5:8
 ibid. IV, 25:55
 ibid. IV,9:23
 ibid. IV,20:39
 ibid. IV,10:25
 ibid. IV,18:35
 1 Cor. 1:23
 St. Augustine, De Doctrina Christiana, Book IV,26:57
 ibid. IV,30:63
 1 Thess. 2:13
 St. Augustine, De Doctrina Christiana, Book IV,27:59