In an essay on the Christian use of the Greek philosophical conception of God ( Basic Questions in Theology, Vol. 2 ), Pannenberg notes that the Platonic tradition only gradually drew the conclusion that God was incomprehensible.   Even Middle Platonists conceived of God as mind, and “thus also knowable to the human mind in one way or another.”

Plotinus is the first to reject the premise (God is mind) and thus the conclusion.  For Plotinus, “the ultimate origin could not be mind because a plurality of knower and known, subject and object, is always posited in mind, so that the mind cannot be the First, the strictly simple One.  Thus, the ultimate origin, the One, must be sought beyond mind.  Therefore, it is unattainable by our mind, inaccessible to our knowledge, and is to be experienced only in ecstasy.”

This suggests several theological conclusions:

First, Plotinus is hinting, negatively, at what comes to fruition in Trinitarian theology. Second, if Plotinus’ argument is sound, then it appears that Trinitarian theology has greater warrant to speak of God as “mind” than Greek philosophy had - since Trinitarian theology teaches a knower and a known.  Third, this suggests that Christian theology also recognizes greater human capacity for knowing God than Greek philosophy.  For if God is both Knower and Known, then He is the archetype of human knowing, and not “beyond knowing.”  Analogy means knowability, and that also suggests that Christian theology is in this sense more “rational” than either pre-Plotinian philosophy (which said God was mind, but denied that we are analogically mind) or Plotinian (which denied God’s knowability by the human mind).

This also gives an important insight into the early Christian use of this philosophical terminology.  If the fathers are giving a Trinitarian gloss to a Plotinian insight (ie, the insight that if God is mind, He must be plural), then their speech about God as “mind” is not a deviation from Trinitarian theology but precisely a Trinitarian claim.