The Beard-Hater and Letters

...are well known to you, though clearly so greatly harassed and derided: Plato, Socrates, Aristotle, and Theophrastus. When that old man Julian refers here to his childhood tutor, Mardonius, who raised him with a strict, traditional education based on the Greek classics. had followed them perhaps too foolishly and simply, and afterward encountered me as a boy burning with the desire to learn, he persuaded me that if I wished to follow in their footsteps, I would become better—not perhaps better than other men (for I would have no contest with them), but certainly better than my own self. I indeed (for what else should I have done?) having obeyed the old man, can now change nothing at all, however much I might desire to; and I blame myself for not opening a free path to all vices.

But there come to my mind those things which the Athenian guest discusses in Plato's works:

He is worthy of honor who commits no sin; but he who even deters others from injury is worthy of more than double honor. For the former is equal to one person, while the latter is equal to many, as he reports the crimes of others to the magistrates. But he who, moreover, joins himself as an ally in punishing injury, this man is a great and perfect man in the state; let him be pronounced the victor in the contest of virtue.
This quote is taken from Plato’s Laws, Book 5. Julian is using it to justify his own philosophical rigor and his later actions as Emperor.

These things that old man taught me. And such, up to that point, was the philosophy of Julian.

Meanwhile, Maximus of Ephesus Maximus was a Neoplatonist philosopher and theurgist (a practitioner of "divine magic") who became Julian's most influential spiritual advisor. came to Nicomedia. He was a philosopher who was later punished with the death penalty by the Emperor Valentinian for his magical arts and impostures. This man was Julian’s second corrupter, and taught him, as Nazianzen Saint Gregory of Nazianzus (c. 329–390 AD), a contemporary of Julian who wrote scathing "Invectives" against him after his death. says, an impiety

original Greek: ὅση τε περὶ ἀστρονομίαν καὶ τὰς γενέσεις καὶ φαντασίαν προγνώσεως τερατεύεται, καὶ τὴν ἑπομένην τούτοις γοητείαν
"that is concerned with astronomy, horoscopes, and the illusions of monstrous predictions, and the sorcery that follows these things."

This school plays tricks with astronomy, birthdays, and the appearance of divination, with magic as their companion. The letters written to Maximus in such honorable terms declare how much Julian always valued this philosopher. From this school, he then moved to Athens

original Greek: καθ' ἱστορίαν τῆς Ἑλλάδος
"to seek out the history of Greece," and...