The word heresy comes from haeresis, a Latin transliteration of the Greek word meaning choosing, choice, course of action, or in an extended sense school of thought. Irenaeus (b. between the years 115 – 125 according to some, or 130 – 142, d. 202) defined heresy as deviation from the standard of sound doctrine.
The Traditional Story
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.