Q. Is there a difference between Ecclesiastes and Ecclesiasticus?
Both names come from ecclesia, an assembly or congregation. Ecclesiastes (Kohelet), traditionally ascribed to King Solomon, is in the Hebrew Bible. Ecclesiasticus, written several decades later by Jesus ben Sira or Sirach, was excluded from the Tanach, though it is quoted in the Talmud.
Chagigah 13a states, “It is written in the Book of Ben Sira (3:21-22), ‘Do not seek things that are too hard for you, do not search out things that are hidden from you. Ponder the things that are permitted to you; you have no need of the things that are secret’”. There is another version of this passage in Midrash B’reshit Rabbah, chapter 8.
Ben Sira wrote in Hebrew; a significant part of his Hebrew original has been found in the Cairo Genizah. The author’s grandson translated the work into Greek. The sages regarded anyone who reads Ben Sira as liable to exclusion from the World to Come (Yerushalmi Sanhedrin 28a) and prohibited a person from having the book in their home (Kohelet Rabbah 12:11).
The opposition to Ben Sira’s work was probably “due to its epicurean and Sadducean tendencies” (Soncino Chagigah, p.73). Kohelet was also under attack by the rabbis but was allowed into the Tanach because “its beginning and end are Torah”.