"It is optional with God to energize externally — but not internally…. God might, or might not, create the Universe; may, or may not, uphold it. But we cannot say that He may or may not be Triune. That immanent and eternal activity which trinalizes the Essence and results in the Three Trinitarian Persons — being grounded in the very nature and constitution of the Supreme Being — must be…. The Spirit, though spirated by the Father and Son, yet proceeds not from the Father and Son as Persons but from the Divine Essence….
"The Father and Son…do not spirate the Spirit from two essences…. They are two Persons, and as two Persons having one numerical Essence spirate…the Third form…of the Essence — the Holy Spirit. Their two personal acts of spiration concur in one single procession of the Spirit. There are two spirations, because the Father and Son are two Persons; but there is only one resulting procession. See Turretin III:31:6….