Augustine’s Tractates on the Gospel of John (In Latin, In Johannis evangelium tractatus) are 124 pieces of writing. Augustine used the word tractate for any prepared spoken communication. Many of these tractates he delivered as homilies or sermons from the pulpit, and they were copied by stenographers in the congregation; others he dictated directly to stenographers in private, but in a way that they could later be read as a homily by others.
All of these tractates were certainly written over the period of the years between 408 and 420. there is agreement that tractates 1-16 were preached by Augustine in the winter of 406-407, and tractates 55 to 124 covering John 13-31 were prepared in 419.
Tractates 55 to 124 are different in style to the earlier tractates, and this has led to the conclusion that they were not spoken to a congregation, but probably to stenographers in private. Certainly, Augustine had long been pressed by people to complete his explanatory coverage of all chapters of the Gospel of John, and accomplished it in this way.
His commentary on the Gospel of John is primarily pastoral rather than consciously being highly theological. Augustine's focus in these tractates is on Incarnation, or the Word made flesh. This is not only a distinctive and important theme in the Gospel of John; it was a significant part of Augustine's own conversion, as mentioned in the Confessions (e.g. Book 7, chapter 9, lines 13-14).