"There was so to speak a work of sapphire [stone]" means that it is translucent with inner truths on that level, and that all things in it are translucent from the Lord. This is clear from the meaning of "a work of sapphire" as the character of the literal sense of the Word when the internal sense is discerned within it, that is, when Divine Truth emanating from the Lord, as it is in heaven, shines through it. For the Word is Divine Truth emanating from the Lord. In origin it is Divine, but as it passes through the heavens it is celestial in the inmost heaven, spiritual in the second or middle heaven, spiritual-natural in the first or lowest heaven, and natural and worldly in the world; this last is its character in the sense of the letter intended for people there. From this it is evident that the sense of the letter, which is the lowest in order, contains a spiritual and a celestial level of meaning, and inmostly the Divine Himself. And since these inner levels are contained in the lowest or literal sense and are seen by those who understand the Word in a spiritual manner, that sense is represented by "a work of sapphire", which lets rays of heavenly light through, that is, which is translucent.
To give some idea of that translucence, let human speech serve to illustrate it. Such speech has its origin in the end a person has in view which he wishes to make known through speech. This end is his love; for a person has what he loves as his end in view. From that end arises the person's thought, and finally his speech. Anyone who stops to think properly about this can see and discern the truth of it. The fact that the end is the primary component of speech is clear from the general rule that all intelligence has an end within it, and devoid of the end it is not intelligence. And everyone knows that thought is a secondary component arising from the first, for nobody can speak without thinking or think without having an end in view. The fact that spoken words ensue from this, and that these are the final component, which is properly called speech, is also well known. All this being so, when a person pays attention to what another utters he pays attention not to the words the speaker uses but to the meaning conveyed by them which is present in the speaker's thought. And one who is wise pays attention to the end in view that has given rise to the thought expressed in speech, that is, he pays attention to what the speaker's aims are and what it is he loves. These three components are present in human speech, in which the spoken words serve as the outward form.
This comparison enables one to gain some idea regarding the Word in the letter. For those in heaven pay attention to the Word in the letter and perceive things there in exactly the same way as anyone is accustomed to perceive a person's thought as it presents itself in spoken words, or in the inmost heaven as anyone is accustomed to perceive a person's aims or end in view. But the difference is that when someone reads the sense of the letter of the Word this is not heard or understood in heaven, only the internal sense, because in heaven they perceive solely the spiritual and celestial levels of the Word, not the natural level of it. The one sense accordingly passes over into the other, for they correspond to each other and only things which have a correspondence have been used in the writing of the Word. All this shows what to understand when reference is made to the translucent nature of the Word, meant by "a work of sapphire"...