The Madness of Prying into God's Secrets

One of Gregory of Nazianzus's cautions in Trinitarian theology relates to the incomprehensibility of the divine processions. Nazianzus is keen to affirm the truth of the processions but just as keen to deny that its specific mechanism or full explanation is within our mental grasp. 

Concerning the eternal generation of the Son: 

How, then, has he been begotten? 

The heavenly begetting is more incomprehensible than your own, to the same extent that God is harder to trace out than Man. . . . Drop your ideas of flux, division and cleavage, drop the habit of treating the incorporeal nature as if it were a body and you might well get a worthy notion of God's begetting. 

How has he been begotten? I re-utter the question with loathing. God's begetting ought to have the tribute of our reverent silence. The important point is for you to learn that he has been begotten. As to they way it happens, we shall not concede that even angels, much less you, know that. Shall I tell you the way? It is a way known only to the begetting Father and the begotten Son. Anything beyond this fact is hidden by a cloud and escapes your dull vision. 

Concerning the eternal procession of the Spirit: 

Insofar as he proceeds from the Father, he is no creature; inasmuch as he is not begotten, he is no Son; and to the extent that procession is the mean between ingeneracy and generacy, he is God . . . What, then, is 'proceeding'? You explain the ingeneracy of the Father and I will give you a biological account of the Son's begetting and the Spirit's proceeding—and let us go mad the pair of us for prying into God's secrets.

—Gregory of Nazianzus, (One God and Christ) Oration 29.8; 31.8.