If anyone is into interesting things...
Everybody likes to post this, but no one makes the connection to Revelation 4:6-11, and Psalm 99:1.
They are cherubs, among the high ranking angels. The forms depicted represent God's pinnacle qualities(wisdom, power, love, and foresight), hence their constant presence around his throne.
But we can't take these visions as literal depictions of angels, because the angels have been shown to be able to take different forms(winged, glowing, or even just human forms). But that is just so a human eye can see them. And furthermore no one knows what a spirit in its true form looks like, which God directly tells Moses at Exodus 33:20.
So why the visions?
To inspire fear and awe. To give an IDEA of forces being dealt with.