The book is a wisdom collection in the manner of Proverbs, but far longer, more personal, and clearly the product of one mind and one setting. Ben Sira ran a house of instruction in Jerusalem, taught young men of the governing class, had travelled, and wrote for a Jewish elite living under Ptolemaic and then Seleucid rule with Greek culture pressing on it. His subjects are what such a life presents: choosing friends, lending money, holding your tongue, behaving at a banquet, dealing with physicians, treating slaves, managing daughters, giving alms, honouring parents, avoiding pride, and handling rulers without being ruined by them. Some of it is worldly to the point of coldness, and some of it, his remarks on women in particular, read badly now and read badly to a good many earlier readers too.
Running through the practical material is a theological claim that made the book important. Wisdom, described as pre-existent and searching the earth for a dwelling place, is settled by God in Israel and identified outright with the Torah, the book of the covenant of the Most High. Wisdom is not an international commodity available to any thoughtful person but a national possession attached to a particular law, a particular people and a particular Temple.
The last quarter is a set piece, the praise of the ancestors, running from Enoch through Noah, Abraham, Moses, Aaron, the judges, David, the prophets and the returned exiles to Simon the high priest, whose appearance in the sanctuary Ben Sira describes as an eyewitness might. It is the earliest sustained attempt to present Israel's history as a sequence of exemplary figures, and it doubles as evidence for which scriptures Ben Sira had in front of him.