The relationship between thought and the spoken word is complex, for it flows in both directions.
The Kabbalah calls this mutual relationship the direct light and the returning light.
From the standpoint of the direct light, there is always descent and constriction; but out of the constriction, the returning light is created, which rises higher than the original, direct light.
A person forms a word, speaks it, and then receives from it.
What he receives from the word does not flow entirely from him, because he himself cannot create a thought that is greater than himself.
We can compare this to a horse and its rider.
Although the horse is subject to the will of the rider, the horse’s greater strength makes it possible for him to lead the rider to places that the rider could not have reached on his own.
… The letters of speech compose a vessel of expression for the thought.
However, the letters have the power to lead that thought and raise it higher than it could have risen by itself.
—Rabbi Adin Steinsaltz