Of God and His Creatures

ho de kurios to pneuma estin, means now the Lord is the Spirit: that is to say, the Lord, mentioned in the previous verse, 16, -- even the Yahweh of Exodus xxxiv, 34, to which that verse refers, -- is the Holy Ghost. This is a statement of the divinity of the Holy Ghost in so many words, as the Greek Fathers elaborately argue, and as St Thomas would not have failed to argue, had he been more familiar with Greek.

Of God and His Creatures: 4.20