4 The Word then is God; and it is also the Word of a stable, unchangeable doctrine, not such as can be sounded by syllables and fleeting, but abiding with the Father, to which abiding doctrine let us be converted, being admonished by the transitory sounds of the voice. For that which is transitory does not so admonish us as to call us to transitory things. We are admonished to love God. All this that I have said were syllables; they smote through the air to reach your sense of hearing, and by sounding passed away: that, however, which I advise you ought not so to pass away, because He whom I exhort you to love passes not away; and when you, exhorted in transient syllables, shall have been converted, you shall not pass away, but shall abide with Him who is abiding.
There is therefore in the doctrine this great matter, this deep and eternal thing which is permanent: whither all things that pass away in time call us, when they mean well and are not falsely put forward. For, in fact, all the signs which we produce by sounds do signify something which is not sound. For God is not the two short syllables “Deus,” and it is not the two short syllables that we worship, and it is not the two short syllables that we adore, nor is it to the two short syllables that we desire to come— two syllables which almost cease to sound before they have begun to sound; nor in sounding them is there room for the second until the first has passed away.
There remains, then, something great which is called “God,” although the sound does not remain when we say the word “God.” Thus direct your thoughts to the doctrine of Christ, and you shall arrive at the Word of God; and when you have arrived at the Word of God, consider this, “The Word was God,” and you will see that it was said truly, “my doctrine:” consider also whose the Word is, and you will see that it was rightly said, “is not mine.”
Source: Tractates on the Gospel of John (New Advent)