Inordinate dici seu conferri vitiis ea quae ordinate in Deo sunt, utpote simplicitas, quae aliquando dicitur pro stultitia, et non est. Apud Deum vero summa simplicitas est. Iuxta hanc regulam et cetera aestimanda sunt.[It is evident that] the things that are in God in an ordered way are [also] spoken of in a disordered way or are compared to vices, as simplicity, which is sometimes put for foolishness, and is not [necessarily] [or “and is not in God in that sense”–see notes in PL]. But for God there is the highest simplicity. Other [words applied to God] too should be judged according to this rule.
One could wish for his Latin to be more fulsome here. Again, a finite verb is missing; I have used that suggested in PL be Arevalo. The phrase et non est is so elliptical as to be difficult to construe; and so on. On other textual matters, I have followed Cazier.
The issues of the Latin aside, however, the point is clear enough. Some words have more than one meaning. “Simplicity” is one of those words. When ambiguous words are applied to God, they should be thought of ordinate, not inordinate. If a word (like “simplicity”) can be used to refer to a vice, it should not be thought of in that way in the case of God. That is the case not only for the word “simplicity,” but for all other words that are applied to God as well. This one instance supplies the rule (regulam) for the others.