Lyric discussion by NovemberSkybot 

Cover art for Vesuvius lyrics by Sufjan Stevens

I think he's referring to Vesuvius as an inner anger/secret. He says it's "all he has." He is holding on to it, and he knows he will eventually let it out, which he sees as failing. The secret is either shameful, or selfish. It is frightening and painful.

His insecurity about releasing this "fire of fire" is not knowing if it's what should really be done (are you ghost/symbol of light), or it's what he's been lead to believe is right (or a fantasy host).

He blames this "Vesuvius" as taking his innocence, something he holds terribly dear. He says it's a tragic oath. It has destroyed what the elegant's(angels?) know. He claims to have "followed men less, but they were the feast of the vermin inblessed(i think he means unblessed/wicked)"

He says though he knows he will fail he can now be made to laugh. Why? As he would rather burn than live in dust, he would treat others this way. He knows he will let out the "fire of fire" held inside to burn those around him rather than bury them in the ashes of a distant explosion (like Pompeii). Thus, it's funny because he feels he has no option. "it has been made to plan"

The panic inside comes from knowing the time is drawing near. He can't ignore the "murdering ghost".

He prays Vesuvius will fall on him now while he is favoring the ghost (believing it to be right thing to do) rather than believing it to be the fantasy host he mentioned earlier, which he seems to be flip flopping between.

"Sufjan fall on the flame or fall on the floor" He is saying be brave and know the pain of being burned and being truthful, or else, you will be as the dust which falls on the floor, burying everything in lies.

"Why does it have to be so hard" Revealing yourself is frightening. You won't know the consequences until you act.