Answer:
   
   The "Merkavah" (Divine "Chariot") visions of Isaiah and Ezekiel are
   difficult to understand; in fact, it is hard to believe that any
   non-prophet can honestly claim to understand them. That said, we can
   eek out odds and ends that have more obvious meanings.
   
   A prophet experiences something of the underlying reality, of heaven.
   Being a person, his mind naturally maps these experiences into
   visions. Metaphors. Much the way the rest of us map ideas into dreams.
   Man relates to G-d in many ways, among them as a subject to a King.
   Therefore, when a prophet sees a vision about G-d, it is quite logical
   that he would see a throne. A large imposing throne that captures the
   attention of the viewer, since the prophet obviously can't form a
   vision that represents G-d Himself. So you'll notice that in the
   vision, He never ends up "looking at" the Occupant. The commentaries
   relate that the "Throne" is on a chariot because G-d was preparing to
   join Israel in their exile. Which is why in that verse in Kings,
   Micaiah described a "Throne" but no chariot. The exile wasn't yet
   imminant.
   
   The three kinds of angel described in Ezekiel's more elaborate
   description of the vision can be understood in the following manner
   (among others): The ofanim (wheels) are the archetype machines. They
   represent the spiritual forces behind man-made things. The chayos are
   named for undomesticated animals, which in turn are called
   "chayah"--living thing; life for its own sake. The contrast to ofanim
   is stark. Chayos are the spiritual forces behind nature. They come
   together and praise G-d, lifting themselves to the level of the
   seraphim. Saraph is to burn. Fire, the least tangible of things, the
   universal representation of the spiritual. Man, by proper utilization
   of the artificial and natural, can elevate them until they too sing
   the glory of G-d no less than do the obviously spiritual.
   
   Holy, holy, holy is the G-d of Hosts. Holiness means being set aside
   for a purpose. Usually we speak of "kadosh le-"; that is, the item
   being santified to something. G-d Himself is as separate from
   everything else as possible, and works entirely toward His own Goal.
   These hosts of forces are what are embodied as angels "to His left and
   to His right".
   
   "G-d of Hosts" refers to the G-d who is Master of all the forces
   throughout existance. The Targum, a 1st century CE commentary and
   Aramaic translation renders the verse: Holy in heaven (the
   "there-ness") on high, the abode of his Presence Holy on earth, the
   work of His Might, Holy for ever, until the ends of time G-d of Hosts,
   the whole universe is filled with His dear Emanation.