From the Gospel of Truth:

For he revealed it as a knowledge with which all its emanations agree, namely, the knowledge of the living book that he revealed to the eternal beings at last as his letters, displaying to them that these are not merely vowels or consonants, so that one may read them and think of something void of meaning. On the contrary, they are letters that convey the truth. They are pronounced only when they are known. Each letter is a perfect truth like a perfect book, for they are letters written by the hand of the unity, since the father wrote them for the eternal beings, so that they by means of his letters might come to know the father.