In the third Theological Oration (= Oration 29), Gregory of Nazianzus argues that divine monarchy does not necessitate rule by only one person.
Gregory claims in 29.2 that there are three ancient opinions about the divine rule of the world: anarchy, polycarchy, and monarchy.
He criticizes anarchy and polyarchy as both tending toward dissolution (λύσις). Polyarchy, he says, is “factious/seditious/quarrelsome” (στασιῶδες) and thus is itself anarchical, and thus is without order, just as anarchy is without order.
He then says this:
ἡμῖν δὲ μοναρχία τὸ τιμώμενον· μοναρχία δέ, οὐχ ἥν ἓν περιγράφει πρόσωπον· ἔστι γὰρ καὶ τὸ ἓν στασιάζον πρὸς ἑαυτὸ πολλὰ καθίστασθαι· ἀλλ’ ἣν φύσεως ὁμοτιμία συνίστησι, καὶ γνώμης σύμπνοια, καὶ ταὐτότης κινήσεως, καὶ πρὸς τὸ ἓν τῶν ἐξ αὐτοῦ σύννευσις, ὅπερ ἀμήχανον ἐπὶ τῆς γενητῆς φύσεως, ὥστε κἂν ἀριθμῷ διαφέρῃ τῇ γε ούσίᾳ μὴ τέμνεσθαι.
But monarchy is what is honored by us. But [it is] a monarchy that one person does not circumscribe–for it is possible even for one [person] being at variance with himself to be rendered many–but [one] that sameness of honor, and union of judgment, and identity of motion unites, and a union with the one of those [who are] from it (which is inconceivable in the case of created nature), with the result that, although there is distinction with respect to number, there is not division with respect to nature. (29.2) 1
One person (e.g., a human ruler) can be divided against himself and therefore can become many (because he loses the unity of himself and introduces plurality); but, in the case of God, there are three persons who share absolute identity of essence, judgment, and motion, and thus constitute the divine monarchy: three persons, one nature.
Gregory reinforces this idea of unity in diversity rhetorically as well: note the threefold repetition of of phrases sharing the same structure but with different nouns, and the number of synonyms meaning roughly the same thing (union, identity, sameness) but expressed by different words.