What is the significance of this vision?
Malbim: After he saw the Raki'a (the divider between Olam ha'Kisei and Olam ha'Chayos), and saw in Olam ha'Kisei "Even Sapir Demus Kisei", i.e. a likeness of the Kisei that appeared like a sapphire stone. Not the Kisei itself, just a likeness of it - the throne special for the King to sit on it to judge straightly and conduct His kingdom. From there goes out conduct of the King of the world and his judgments. The Kisei is made from sapphire stone. Its appearance is clear, like a glass or mirror in which one sees what is opposite it. So matters of Elokus in Olam ha'Sefiros above Kisei are in light.
Why was there a human image above?
Malbim: This is like one who looks in a mirror and sees the sun - he does not see the sun itself, only an image in the mirror. So in the vision of the sapphire stone, he saw that high above the Kisei is a human image. It is Atzeilus of Sefiros in which His glory is clothed in light. It is the root of conduct of His world. The Nevi'im, in their great power, equated the form to its Former (Midrash]. Hashem arranged the ties of conduct of existence, and the great man is attributed to the small man, whose Nefesh is Atzulah 1 from the cornerstone above, from Olam ha'Kisei. The root of his Neshamah is above with the King in His work - "Na'aseh Adam b'Tzalmenu" (Bereishis 1:26). He saw only Demus (a likeness), for a likeness of conduct via Chachmah, Binah and Da'as, and Midos such as Chesed, Din and mercy. All is like man's glory. He did not see in Olam ha'Atzeilus itself, only in a mirror. He saw an image of man in the Navi's Nefesh tied to all his powers and Midos, and how he conducts his Nefesh with its small Merkavah. He depicts that so Hashem conducts His big Merkavah. The big world and small world correspond to each other. Hashem is the Nefesh of the worlds and their Conductor; Yechezkel saw Him riding the Merkavah. This parallels man's Nefesh and its conduct of the body.
This is an emanation from a source, in which nothing is detracted from the source, e.g. something ignited from a flame. (PF)