Exode 24:10

And Nadab and Abihu lifted up their eyes, and saw the glory of the God of Israel; and under the footstool of His feet which was placed beneath His throne, was like the work of sapphire stone a memorial of the servitude with which the Mizraee had made the children of Israel to serve in clay and bricks, (what time) there were women treading clay with their husbands; the delicate young woman with child was also there, and made abortive by being beaten down with the clay. And thereof did Gabriel, descending, make brick, and, going up to the heavens on high, set it, a footstool under the cathedra of the Lord of the world whose splendour was as the work of a precious stone, and as the power of the beauty of the heavens when they are clear from clouds.

AND THEY SAW THE G-D OF ISRAEL. Rabbi Abraham ibn Ezra explained: “They saw Him in a prophetic vision, this being similar to the verse: I saw the Eternal standing beside the altar. — And there was under His feet the like of a paved work of sapphire stone. This is identical with what the prophet Ezekiel saw: as the appearance of a sapphire stone was the likeness of a throne. — And the like of the very heaven for clearness, means that they saw under the paved work of sapphire stone the likeness of the very heaven for clearness, which is identical with the firmament, like the color of the terrible ice, stretched forth, Verse 22. over the heads of the living creatures [that Ezekiel saw]. Now here it is written, And they saw the G-d of Israel, and there it is written, This is the living creature that I saw under the G-d of Israel., 10:20. [In saying that he saw the living creature under the G-d of Israel, the prophet Ezekiel] used a shortened expression, for the living creature was under the firmament which was under the throne, and all this was under the Glorious Name.” [Thus far is Ibn Ezra’s language.]
In line with the simple meaning of Scripture the expression the G-d of Israel is used here to indicate that the merit of their father Israel [Jacob] was with them, and it was through his merit that they beheld this vision. And by the way of the Truth, [the mystic doctrine of the Cabala], it is because Scripture mentioned at the Giving of the Torah, and G-d spoke, this being identical with the verse, Behold, the Eternal our G-d hath shown us His glory and His greatness, and we have heard His voice out of the midst of the fire, therefore Scripture explained here that they saw the G-d of Israel. It does not say as it does in all other places, the Eternal, the G-d of Israel, but mentioned this [the G-d of Israel] in order to say that the seventy elders perceived in this vision more than the rest of the people who saw upon the earth His great fire, because the people saw through a partition of cloud and thick darkness., 5:19. Onkelos hinted at this, for he translated here, “and they saw the Glory of the G-d of Israel,” but did not render it, “and the Glory of G-d revealed itself to them,” as is his way of translating in other places., Onkelos translated: “and the Glory of the Eternal revealed itself…” Here, however, he wrote “and they saw,” in order to indicate that they achieved a greater insight in this vision than the rest of the people.

ויראו את אלו-הי ישראל, just as the Torah described “G’d’s “back” becoming visible to Moses in Exodus 33,23 so the meaning of the elders “seeing” means that the manifestations of G’d’s attributes they had experienced made Him as real to them as if they had seen Him with their physical eyes.

לבנת, the whiteness of

וכעצם, the appearance. The construction is similar to Lamentations 4,7 אדמו עצם מפנינים, “their bodies were like sapphires.”

לטהר, as when the sky is clear without clouds.

ותחת רגליו, on the earth, the lowest point. We have G’d on record as describing “earth” in such terms in Isaiah 66,1 והארץ הדם רגליו, “the earth is My footstool.”

כמעשה לבנת ספיר, an essence, totally transparent, devoid of colours and permanent contours so that it is almost completely abstract, capable of absorbing spiritual input from spiritual domains at will. An allegorical description of the human נפש, “life-force.”

וכעצם השמים לטוהר, they perceived that this לבנת הספיר, “essence,” is totally independent of the raw material man is made of; just as what we perceive as the essence of heaven in the sky is totally devoid of tangible matter. It is the essence of what we consider the celestial regions, “heaven,” for lack of a better word. It is not connected to the solid physical planets etc., which form the “inhabitants” of these celestial domains. The fact that the “sky,” “heaven,” has no physical dimensions makes it appear as if it is the spiritual dimension of “Heaven” itself.