Donald Frew, Wiccan author and elder, has pointed out that both Platonism and Hermeticism are important sources of (modern) Pagan ideas. In this interview (which is taken from the book Modern Pagans) Frew specifically mentions the writings of Porphyry, Iamblichus, Julian ("the Apostate"), and Proclus, along with the Corpus Hermeticum, as among "the oldest written sources for Pagan theory and ritual". In an article he wrote for the Academic journal Ethnologies Frew provides a more detailed argument to support his contention that much of "the roots of Wicca can be found in the writings of the late Roman Neoplatonists."I want go a bit further than Frew and show that basic Wiccan ideas can be traced back to Plato himself, who lived six centuries before Plotinus, and also to the Stoic philosophers, whose school is almost as old as Plato's.
It is unfortunate that modern writers, including even a Pagan like Frew, continue the misguided practice of referring to Plotinus, Porphyry, Iamblchus, Julian, and Proclus as "Neoplatonists". The inevitable implication of the use of the term "Neoplatonists" is that many of the ideas of these later Platonists, especially their more mystical and religious ideas, are not genuinely Platonic. The prefix "neo" is affixed precisely in order to insinuate that Plato's own writings were neither mystical nor religious in any way. In fact, all of the philosophers labeled by scholars as "Neoplatonists" referred to themselves simply as Platonists, and their philosophical writings were based solidly on Plato's. Therefore the term "Neoplatonist" should be rejected as anachronistic and misleading, and, for that reason, I will consistently refer to Plotinus, etc, using the terminology they themselves used: Platonists.
Let's start with the Wiccan Rede: "An it harm none, do as you will." The exhortation to "harm none" comes straight from the most famous of all of Plato's dialogues, the Republic. As classicist Robin Waterfield states in his own translation of the Republic, "Socrates finally concludes that it is never right to harm anyone under any circumstances." (See his commentary on p. 8 of that book.) It is especially significant that Waterfied is here commenting on the first book of the Republic, and that the remaining nine books are largely devoted to defending this conclusion. This same idea is found in other Platonic dialogues as well, especially the Crito and the Gorgias.But what about "do as you will"? It turns out that the clearest expression of this admonition is found not among the writings of Plato, but among the Stoics. For it was the Stoics who taught that:
"They are free who live as they will; who are not subject to compulsion, to restraint, or to violence; whose pursuits are unhindered, their desires successful, their aversions unincurred."
The Stoics not only provide an ancient and highly respectable pedigree for the second half of the Wiccan Rede, they also provide a strong argument for how the two parts of the Rede are connected:"Who, then, would wish to lead a wrong course of life? No one. Who would live deceived, erring, unjust, dissolute, discontented, dejected? No one. Wicked persons, then, do not live according to their own wills; therefore no such person is free."
Both of the above quotes are taken from the Discourses of Epictetus, book IV, section 1.
At the risk of being repetitive, let me summarize. The Wiccan Rede really has three components: (1) to "harm none", (2) to "do as you will", and (3) the implication that these two admonitions are connected with each other, or at least compatible with each other. The writings of Plato provide multiple examples of the first idea, while the writings of the Stoics provide an ancient philosophical basis for all three. In fact, as the last quote from Epictetus shows, we can only truly be free (that is, do as we "will"), when we act justly and rightly, and that anyone who is deceptive, unjust, etc, is not truly free.
Finally it should be noted that the second quote from Epictetus is actually a restatement of one of the most famous and singular teachings of Socrates: that no one ever does wrong knowingly. The Socratic world view had no place in it for "evil" as a fundamental principle. For Socrates, Plato, and the Stoics the Cosmos is fundamentally "good", and all apparent "evil" is only the result of our ignorance. This radical view of the Cosmos teaches us that if we so choose, each of us is capable of living in a way that is beneficial to ourselves and to our fellow creatures, and that is also in accordance with our own wills, and that, moreover, living in such a way is the only way to be truly free.