De + the Ablative Case (Brief Remarks About Latin)

Cyprian of Carthage uses patre (ablative singular of pater) with the preposition, de. I guess the whole expression is "De Patre et Filio et Spiritu Sancto scriptum est - Et hi tres unum sunt." So, a question arises concerning what kind of ablative this construction is.

De + the ablative is a standard construction in Latin and it frequently occurs among the ante/post-Nicene Fathers. I teach students about de re and de dicto utterances; many of the ecclesiastical works in Latin also have de + the ablative constructions. For instance, De Trinitate by Augustine of Hippo, Novatian of Rome and Hilary of Poitiers, also De Civitate Dei by Augustine and so forth. Other familiar constructs are de facto and de jure.

De + patre can be rendered "of, about, concerning or regarding the Father." Basil Gildersleeve calls this usage, an ablative of object (section 417.5), which he distinguishes from the ablative of reference ("according to"). Another source classifies de + the ablative as a figurative use of de since the preposition is used elsewhere to reference a literal place (e.g., dē caelō dēmissus). See https://dcc.dickinson.edu/grammar/latin/uses-prepositions#rfn3

There is also a good explanation here: https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0059%3Aalphabetic+letter%3DD%3Aentry+group%3D3%3Aentry%3Dde2

Lewis and Short explain that de + the ablative eventually came to replace the genitive and its object: they write that de along with the ablative is able to "indicate the thing with reference to which any thing is done, with respect to, concerning."