Reasons 1-3: order of the universe; supreme unity/truth/goodness; if many, absurdities
The first is taken from the order of the universe's parts. Where there is order, there must be something one to which the rest are reduced. Aristotle: a plurality of rulerships is not good; let there be one ruler. Athanasius: a multitude of gods is a nullity of gods.
THE SECOND: God is highest unity, highest truth, highest goodness, which cannot be except unique and pure.
THE THIRD: if there were many gods, they either differ altogether, or are altogether one, or partly both: the first is absurd; if the second, they were already not many but one.
Latin
PRIMA sumitur ab ordine partium universi. Ubi ordo est, unum esse aliquid oportet ad quod cetera reducantur. Aristoteles: Non est bonum pluralitas principatuum: unus princeps esto. Athanasius: Multitudo deorum nullitas est deorum. SECUNDA: Deus summa est unitas, summa veritas, summa bonitas, quae non potest esse nisi unica & pura. TERTIA: si plures dii sint, aut omnino differunt, aut omnino unum sunt, aut partim differunt partim unum: primum absurdum; si alterum, jam non plures sed unus.