This is the meaning of the verse: “...and through the word of God the heavens were made” (Psalms 33:6). For initially there is the thought – Adam Kadmon – but this is concealed. The revelation of thought comes about through speech, which consists of letters. Whatever is concealed in thought must enter into the category of speech in order to be revealed.
However, the component parts and organizing principles of thought are by no means identical with those of speech, for a thought is in the mind, whereas in speech we express our thoughts in words and letters. In order to communicate what is in our minds, what is conceived in thought must be submitted to the rules of language and cast in the form of letters and words. The same applies in the upper worlds.
The first order is that of thought. Its revelation comes about through speech. What is conceived in the mind within the parameters of thought can come forth in speech only within the parameters of speech, namely through the letters.