Cicero's purpose in this passage is to advise and guide his son, Marcus, on the importance of a well-rounded education that combines both Greek and Latin studies. He encourages Marcus to continue his philosophical studies under Cratippus in Athens while also recommending the reading of Cicero's own philosophical books to enhance his command of the Latin language.
Cicero emphasizes the value of combining oratorical skills with philosophical knowledge, presenting himself as an example of someone who has excelled in both areas.
The textual evidence supporting this purpose is found in Cicero's recommendation for Marcus to read not only his orations but also his philosophical works, asserting that his philosophical style, though different from his orations, is worth cultivating for a comprehensive mastery of language and expression.
Cicero's intention is to guide Marcus in becoming not just a philosopher but a well-spoken and eloquent individual.