Judah the Pious, Dan, Studies, p. 153

Jewish Mysticism
Moses alone saw the great glory. Thus [it says in Scripture] “And the Lord [YHWH] spoke to Moses,” “And the Lord [YHWH] said,” using this name [YHWH]. Therefore Jethro said- “Now I know that the Lord [YHWH] is greater than all gods” (Exod. 18-11). The Lord is unique, He is God of gods, He and not an angel. At times [YHWH] is used as the name of His essence (shem ‘asmo), referring to the Creator, and at times it refers to the form (ha-to’ar) that appears to the prophet. It has already been written in the Sefer ha-Kavod [“Book of the Glory”] that the form is according to the decrees [of God’s will]. It says [in Scripture] “I am the Lord.” Does He appear to the prophet in such a way? The testimony and proof is in the expression “the Lord of hosts,” i.e., He appears as a form within the [celestial] hosts, as in the case of Michaiah, Isaiah, and Daniel.

Translated by Elliot Wolfson in Through a Speculum that Shines- Vision and Imagination in Medieval Jewish Mysticism, Princeton- Princeton University Press, 1994.