"One of the seven Old Testament books rejected by Martin Luther and subsequent Protestants was the book of Ecclesiasticus, alternatively known by its “Old Latin” title Sirach." [source]
Well, why according to pop-Romanism?
"Hence, we see that all the arguments generally made against Ecclesiasticus, namely that it was unknown by Christ and the Apostles, is utterly false. The book’s general reception and circulation in the Patristic era also testifies to its divine origin." [source]
Luther's Preface to the Book of Jesus Sirach 1533
This book has heretofore carried the Latin title, Ecclesiasticus, which has been understood in German to mean “spiritual discipline.” Through reading, singing, and preaching it has been extensively used and inculcated in the churches, yet with little understanding or profit except to exalt the estate of the clergy and the pomp of the churches.
Its real name is otherwise Jesus Sirach, after its author as its own prologue and the Greek [50:27] indicate. This is how the books of Moses, Joshua, Isaiah, and all the prophets are named, after their authors. Yet the ancient fathers did not include this one among the books of sacred Scripture, but simply regarded it as the fine work of a wise man. And we shall let it go at that.
Since [the translator] admits in the prologue that he came to Egypt in the reign of King Euergetes and that he there completed this book (which his grandfather had originally begun), it seems to us that he has compiled the best from as many books as he could find. After all, there was a valuable library in Egypt which had been founded by the father of Euergetes, King Philadelphus. Moreover in those days both books and learned men were held in high esteem; and, having come from all over, especially from Greece, they constituted one great school of learning [in Alexandria]. There, too, the Jews had built a temple and instituted divine worship.
That the book must be a compilation is suggested also by the fact that in it one part is not fitted neatly to the next, as in the work of a single author. Instead it draws on many books and authors and mixes them together, much as a bee sucks juices out of all sorts of flowers and mixes them. Moreover, as one may deduce from Philo, it appears that Jesus Sirach was descended from the royal line of David, and was either a nephew or grandson of Amos Sirach, the foremost prince in the house of Judah, living some two centuries before the birth of Christ, about the time of the Maccabees.
This is a useful book for the ordinary man. The author concentrates all his effort on helping a citizen or housefather to be Godfearing, devout, and wise; and on showing what the relationship of such a man should be to God, the Word of God, priests, parents, wife, children, his own body, his servants, possessions, neighbors, friends, enemies, government, and anyone else. So one might well call this a book on home discipline or on the virtues of a pious householder. This indeed is the proper “spiritual discipline,” and should be recognized as such.
Should anyone like to know what labor it cost us to translate this book, let him compare our German with all the other versions, be they Greek, Latin, or German, old or new—the product will bear sufficient testimony concerning those who produced it. In all languages so many wiseacres have gone at this book that—quite apart from its inherent lack of order from the very outset—one should not be surprised if it turned out completely unrecognizable, unintelligible, and in every respect worthless. But we have put it together again like a torn, trampled, and scattered letter, and washed off the mud; we have brought it into shape as anyone can see for himself. God be praised and thanked. Amen. Christians will not criticize us for this, but the world will; in keeping with its virtues, it will manage to thank us as it has always done. [LW 35:347-348]
"One of the reasons Roman Catholics argue for a broader canon is that the oldest extant manuscripts of the Septuagint do contain a number of Apocryphal books. These manuscripts are: Vaticanus (early 4 th century), Sinaiticus (early 4 th century), and Alexandrinus (early 5 th century). The Apocryphal books of Wisdom, Ecclesiasticus, Judith and Tobit are included in all three, but there are also differences. Vaticanus does not include any of the Maccabean books, while Sinaiticus includes 1 and 4 Maccabees and Alexandrinus includes 1, 2, 3, and 4 Maccabees and a work known as the Psalms of Solomon. If inclusion of a book in the manuscript proves its canonicity, as Roman Catholics assert, then 3 and 4 Maccabees were canonical." [William Webster, Holy Scripture: The Ground and Pillar of Our Faith, Volume II, p. 320]