Celsus, again, having perhaps misunderstood the words, “For the mouth of the Lord has spoken it,” or perhaps because some ignorant individuals had rashly ventured upon the explanation of such things, and not understanding, moreover, on what principles parts called after the names of the bodily members are assigned to the attributes of God, asserts: “He has neither mouth nor voice.” Truly, indeed, God can have no voice, if the voice is a concussion of the air, or a stroke on the air, or a species of air, or any other definition which may be given to the voice by those who are skilled in such matters; but what is called the “voice of God” is said to be seen as “God's voice” by the people in the passage, “And all the people saw the voice of God;” the word “saw” being taken, agreeably to the custom of Scripture, in a spiritual sense.
Moreover, he alleges that “God possesses nothing else of which we have any knowledge;” but of what things we have knowledge he gives no indication. If he means “limbs,” we agree with him, understanding the things “of which we have knowledge” to be those called corporeal, and pretty generally so termed. But if we are to understand the words “of which we have knowledge” in a universal sense, then there are many things of which we have knowledge, (and which may be attributed to God); for He possesses virtue, and blessedness, and divinity.
If we, however, put a higher meaning upon the words, “of which we have knowledge,” since all that we know is less than God, there is no absurdity in our also admitting that God possesses none of those things “of which we have knowledge.” For the attributes which belong to God are far superior to all things with which not merely the nature of man is acquainted, but even that of those who have risen far above it. And if he had read the writings of the prophets, David on the one hand saying, “But You are the same,” and Malachi on the other, “I am (the Lord), and change not,” he would have observed that none of us assert that there is any change in God, either in act or thought.
For abiding the same, He administers mutable things according to their nature, and His word elects to undertake their administration.
Source: Against Celsus (New Advent)