The four books of St. Augustin On Christian Doctrine (De Doctrina Christiana, iv libri) are a compend of exegetical theology to guide the reader in the understanding and interpretation of the Sacred Scriptures, according to the analogy of faith. The first three books were written a.d.397; the fourth was added 426. He speaks of it in his Retractations, Bk. ii., chap. 4, as follows: "Finding that the books on Christian Doctrine were not finished, I thought it better to complete them before passing on to the revision of others. Accordingly, I completed the third book, which had been written as far as the place where a quotation is made from the Gospel about the woman who took leaven and hid it in three measures of meal till the whole was leavened. I added also the last book, and finished the whole work in four books [in the year 426]: the first three affording aids to the interpretation of Scripture, the last giving directions as to the mode of making known our interpretation. In the second book, I made a mistake as to the authorship of the book commonly called the Wisdom of Solomon. For I have since learnt that it is not a well-established fact, as I said it was, that Jesus the son of Sirach, who wrote the book of Ecclesiasticus, wrote this book also: on the contrary, I have ascertained that it is altogether more probable that he was not the author of this book. Again, when I said, 'The authority of the Old Testament is contained within the limits of these forty-four books, ' I used the phrase 'Old Testament' in accordance with ecclesiastical usage. But the apostle seems to restrict the application of the name 'Old Testament' to the law which was given on Mount Sinai. And in what I said as to St. Ambrose having, by his knowledge of chronology, solved a great difficulty, when he showed that Plato and Jeremiah were contemporaries, my memory betrayed me. What that great bishop really did say upon this subject may be seen in the book which he wrote, 'On Sacraments or Philosophy.'"