The Aristeas purpose was really to establish and defend the authority of this Greek translation of the Pentateuch. That purpose lies implicit in much of the letter. It comes to the fore, near the end, in the description of the public reading and ratification of the translation:
Most of the scholars today —who are now in the majority—disagree.  They contend that it is much more likely that the Jewish community itself instigated the translation to serve their own liturgical and pedagogical needs. When scholars holding this position reinvestigate Ptolemy’s supposed interest in a Greek translation of Jewish Law, the evidence begins to evaporate.
It often comes as a surprise to laypeople to learn that ancient copies of the Bible vary, sometimes in minor ways, but sometimes, also, in important ways. Variation exists between any two manuscripts of the Bible, even when they are written in the same language. But apart from minor variations among ancient manuscripts, when all the evidence from antiquity is compared, two important traditions of the biblical text emerge. They are the Masoretic text and the Septuagint.