It is estimated that Augustine preached about 8,000 times during his long life. Copies still exist of between 400 and 500 of these sermons. Most of these sermons were taken down by scribes as he preached without the use of a prepared script. They are a faithful stenographic record of what Augustine actually said, with probably no subsequent editing of them by himself. Persons who could not attend his homilies wanted copies of them.
For Augustine, allowing his sermons to be written down by stenographers was the most efficient means for him to transfer his thoughts into written records. They contain a total of 1,500,000 words and comprise almost a third of his surviving works. As could be expected, they cover a wide range. Many are simple expositions based on the Scripture readings of the Mass that were laid down by the Church's liturgical calendar of that era. As well, Augustine as bishop and chief pastor sometimes instituted a series of catechetical sermons, or a number of sermons around a particular theme.
Professor James O'Donnell at Georgetown University in Washington D.C. noted that there are sermons on all 150 Psalms, deliberately gathered by Augustine in a separate collection, Enarrationes in Psalmos (392-418: Enarrations on the Psalms). O'Donnell proposes that these are perhaps the best work of Augustine as a homilist, for he found in the uplifting spiritual poetry of the psalms many messages that he could apply consistently to his view of an austere and practical Christian Faith that was also time full of hope.
At a higher intellectual level are his sermons in the series called Tractatus in evangelium Iohannis 124 ("Tract on the Gospel of John"), which amounts to a full commentary on this, the most philosophical of the four Gospels. Other sermons range over much of Scripture. O'Donnell noted that Augustine had little to say about the prophets of the Old Testament, and what he did have to say about Paul appeared in his written works rather than in his public sermons.
What do the sermons of Augustine reveal about his preaching?
When preaching to the local people of Hippo, he was more likely to preach simply, and the congregation would have drawn spiritual support from his words. There is often beauty, playfulness, and brilliant imagery in the selection of language by Augustine. Using his intellectual and rhetorical abilities, he made some marvellous Latin puns - for example: non gente, sed mente, which translates into English somewhat clumsily as "not what your ancestors have wrought but what you have thought."
One very lengthy sermon was preached on the occasion of the pagan feast of the Kalends of January, the Feast of the New Year, in 404. It is 1,546 lines in length which means that Augustine on that day preached for more than two and a half hours.
What do the sermons offer that his books do not already offer?
These sermons allow us to hear Augustine "live and uncut", as some television programs of today claim to be. In these sermons Augustine is captured going about his everyday work as a preacher to a local congregation, and his relationship with that congregation is on display. Had the sermons of Augustine his only words that remained available to us today (and not, in truth, merely the most overlooked third of his works that still exist), they would be much more valued and studied.
Augustine’s Christmas Sermon 188. For the Feast of the Nativity. http://www.dec25th.info/Augustine's%20Sermon%20188.html
Living Six Months with St. Augustine. A journalist in Texas writes of his experiences and impressions in reading all of Augustine’s sermons in a six-month period. http://www.catholic.org/news/saints/story.php?id=47435
St Augustine’s Sermon 46 On Pastors. He urges the shepherds of Christ’s flock to seek out the lost and straying sheep; he is reflecting on the book of the prophet Ezekiel. https://www.crossroadsinitiative.com/library_article/251/Seek_Out_the_Lost__St._Augustine.html AN2150