When a circle is seen in the vision of the Chariot, the immediate inference is that this is a radiation of light (הארה, he’arah) that shines in a general, undifferentiated way. It encompasses all the created realms and beings, and accordingly takes the form of an encompassing sphere or circle, inasmuch as it encompasses and shines to the entire existence contained within it without any differentiation. Thus the Supreme Will maintains this lowly world in existence through a general providence which makes no differentiation between one species and another or between one individual and another, but which encompasses all the created realms and beings equally.
The Circle Seen in Ezekiel's Chariot Vision
Kalach Pitchei Chokhmah 13:11