Mirror mirror on the wall

I've been listening to some music and I ran into this line of lyrics in a song:

Mirror mirror
On the wall
Show me the truth:
Of them all
Which one am I?

I kind of get the meaning of the phrase, but somehow it seems gramatically weird. Could anybody please explain to me why this phrase is correct? Or incorrect? Thanking you!:)

The speaker is addressing the mirror, by name: in Snow White, where this originates, the mirror is magic and can talk.

It really should have some extra punctuation, eg "Mirror, Mirror, on the wall, show me the truth...".

It's like saying "Mary, Mary, quite contrary, how does your garden grow?" which is a nursery rhyme, or "Tom, Tom, my old pal, fancy a beer?" (which isn't).