Georgius Gemistus who lived from around 1355 to 1454 CE, was a latter day Neoplatonic philosopher born in Constantinople. Gemistus expressed his loyalty to Plato by changing his name to Pletho or Plethon meaning "full". It is under this name that he is known as the author of De Differentiis/Differentia, a comparison between Plato and Aristotles' concepts of God.
Several Pletho manuscripts came into the possession of his former student, Cardinal Bessarion. Bessarion in turn willed his collection to Venice's San Marco library and among the books and manuscripts authored by Pletho was the Summary of the Doctrines of Zoroaster and Plato, a summary of the Book of Laws, which was a blending of Pletho's own beliefs with what he understood to be the beliefs propounded by Plato and Zoroaster.
The following are annotated excerpts from the Summary based on the translation by Darien C. DeBolt, University of Oklahoma:
"These are the principal doctrines that ought to be acknowledged by one who will be prudent. The first of these is one about the divinities: that they are. One of the divinities is the supreme sovereign (Zeus), both the greatest and the best that it is possible to be. The supreme sovereign is set over this whole order; singular in highest divinity; being in its entirety and completely ungenerated; both progenitor and highest creator of all. [Our note: here we find acknowledgement of a singular ultimate uncreated creator. This sentiment is largely congruent with Zoroastrianism. We omit mention of the Olympian and Tartarean gods - a Hellenic concept. The former are rulers of the heavens while the latter are rulers of mortal creation.]
"The supreme sovereign (Zeus) alone in the singularity of the highest divinity, governs apart over the universe." [Our note: This may be interpreted as an panentheistic doctrine.]
"The divine are not responsible for any evil, neither to any other in the universe nor to us. They are responsible for all goodness. [Our note: this separation of the Creator God from the creation of, or being the cause of evil is a concept that developed in Zoroastrianism.]
"Everything that emanates from the Supreme Creator (Zeus) by an unalterable and inexorable destiny, effects its purpose in accordance with the best. [Our note: this concept is also congruent with Zoroastrianism.]
"Concerning the universe, first this universe is eternal. This universe was begotten by the Supreme Creator (Zeus); it was neither begun in time nor will it come to an end. [Our note: If creation is eternal at both ends, i.e. without beginning or an end, then the concept creation introduces a beginning which violates this concept. What we read here is that Pletho avoids this discrepancy by stating that the act of creation first took place before the creation of time (and presumably therefore beyond the limits of time and ultimately eternal). There is limited congruence here with Zoroastrian-based Zurvanism and with the Zoroastrian concepts of unlimited and limited time - time of very long, quasi-eternal, duration, but one that nevertheless has a beginning and an end. Therefore, Zoroastrianism does envisage an end time - at the end of limited time - when all souls will return to God.]
"Next that from the many universes it was joined into a unity. [Our note: a fairly profound statement.]
Next that the best out of those possible has been made, precisely because it was made by the particularly best being. Once it had been made, it was such that nothing had been left out and anything added to it would be excessive. [Our note: this statements appears to assert an inherent perfect creation which belies the degradation of creation in gnostic statements in the Oracles of Zoroaster.]
"In addition to these things, that just as it was set down in this form so it shall always be preserved undisturbed. These then are the doctrines about the universe.
"Concerning ourselves, first our soul, being of divine origin, is immortal and remains in this universe the whole time and is eternal. [Our note: see our note above regarding time and the return to God at the end of limited time.]
"The soul is sent down for the purpose of partaking in a mortal body here each time by the divine, at one time in one body, at another in another, on account of the harmony of the universe. That, even though we have a share in mortal things, one thing in us is from the immortals and this is our form. In this way, the universe itself is united to itself. [Our note: We have here a belief in reincarnation that is not found in Zoroastrianism.]
"Next that the good is in us, naturally by our ties to the divine, and this is the fit end of life. [Our note: The first part of this statement is congruent with Zoroastrianism. The second part bears further contemplation and understanding. If it means that in the end, the inherently good soul will reunite with the goodness of the divine, that concept has some congruence with Zoroastrianism.]
"In addition to all this, that our happiness is in our immortal part, put there by the divine who unite our kind, and that is the substance and most important part of man.
"These then are the principal doctrines concerning the divine, this universe, and our nature. If one, motivated by prudence about considerations of what is necessary, will also really be prudent, then one ought to acknowledge and be mindful of these things."