When the book of Ezekiel opens, the first two units (chapters 1-7 and 8-11) consist of back-to-back visions of God's throne-chariot, carried by the cherubim. In chapter 1, Ezekiel takes his time describing the cherubim, but when his account moves to the throne itself, he becomes vague and sketchy:
And above the dome over their heads there was something like a throne, in appearance like sapphire; and seated above the likeness of a throne was something that seemed like a human form. Upwards from what appeared like the loins I saw something like gleaming amber, something that looked like fire enclosed all round; and downwards from what looked like the loins I saw something that looked like fire, and there was a splendor all round. Like the bow in a cloud on a rainy day, such was the appearance of the splendor all round. This was the appearance of the likeness of the glory of the LORD. When I saw it, I fell on my face, and I heard the voice of someone speaking.
(Ezekiel 1.26-28, NRSV)
Ezekiel sees a man-like figure sitting on a throne-like thing, looking sapphire-like, amber-like, fire-like, surrounded by something rainbow-like. All of this is:
the likeness of the glory of the LORD.
Commenting on the opening chapter, Joyce1 offers:
Ezekiel affirmed nothing less than the presence of the God of Israel in alien Babylonia, far from the temple site. This is a bold gambit, and this boldness is reflected in the note of awkwardness that seems to attend the claim. Unambiguous indeed, but note the circumlocution of v. 28: "such was the appearance of the likeness of the glory of the LORD." There are at least three levels of circumlocution here (at least three, because it would be a mistake to imagine that the tetragrammaton itself is ever an exhaustive and univocal summation of the deity).
Calaway2 briefly makes the connection between Ezekiel's shifty description of his vision of God with the thematic content of the opening chapters of the book:
Ezekiel 8:3 uses "form" as a circumlocution to avoid giving direct apprehension of God. In this passage, the glorious human-like figure reveals to Ezekiel the abominations in the temple and why God's glory (כבוד) has left the Jerusalem temple. In the process, the word תבנית appears in the realm of the circumlocutions surrounding the "glory of the LORD", which allows one to communicate with God through a vision of an aspect of God, his "glory," which has a luminous human-like appearance. Distancing terminology abounds in Ezekiel's visions of God and his retinue, including terms such as "form" (תבנית), "appearance" (מראה), and "likeness" (דמות).
In other words, the opening chapters of Ezekiel consist of a visionary revelation from God concerning the spiritual state of Jerusalem, including the exit of God's glory from the temple. But the prophet plays it safe to strenuously express that he is not seeing God himself.
Ezekiel uses deliberately distant language (form, appearance, likeness) when describing his vision of God in the opening chapter. He then proceeds to add another layer of distance by insisting he is not seeing 'YHWH' himself, but a visual representation of 'the glory of YHWH', the very glory that has left the temple in Jerusalem.
1 Paul M. Joyce, Ezekiel: A Commentary (2009), p. 74-75.
2 Jared C. Calaway, The Sabbath and the Sanctuary (2013), p. 123, footnote 73.