From his lectures on Genesis:
(God) does not speak grammatical words; He speaks true and existent realities. Accordingly, that which among us has the sound of a word is a reality with God. Thus sun, moon, heaven, earth, Peter, Paul, I, you, etc. – we are all words of God, in fact only one single syllable or letter by comparison with the entire creation. We, too, speak, but only according to the rules of language; that is, we assign names to objects which have already been created. But the divine rule of language is different, namely: when he says: “Sun, shine,” the sun is there at once and shines. Thus the words of God are realities, not bare words.
I love that last line. It drives home, not only the difference between our words and God’s Word, but also the difference between the word of man, which is changeable and, according to post-modern theory, given meaning only as the hearer understands the word, and the Word of God, which does not merely connote a thing, but is the thing itself. (Take that, Immanuel Kant!)