Albert Barnes Commentary Exodus 24:10

"And they saw the God of Israel; and there was under his feet as it were a paved work of sapphire stone, and as it were the very heaven for clearness." — Exodus 24:10 (ASV)

And they saw the God of Israel - As they ate the sacrificial feast, the presence of Yahweh was manifested to them with special distinctness. In the act of solemn worship, they perceived that He was present with them, as their Lord and their Deliverer.

It is idle to speculate on the mode of this revelation. That no visible form was presented to their bodily eyes, we are expressly informed (Deuteronomy 4:12); see (Exodus 33:20); compare (Isaiah 6:1).

The latter part of this verse may be read: under His feet, it was like a work of bright sapphire stone, and like the heaven itself in clearness. On the sapphire, see (Exodus 28:18); compare (Ezekiel 1:26). The pure blue of the heaven above them lent its influence to help the inner sense to realize the vision which no mortal eye could behold.