Becoming Closer
Hail and Fire, mixed with Blood
nTrumpet - call to war
nSymbols of divine wrath
•Plagues of Egypt
•Isaiah 10:17
nTrees:  great men?
nLindsey:  ICBMs
nAlaric the Goth
A trumpet is, among other things, a call to war.  This passage is sufficiently bloody and destructive to view it that way, and this is unchallenged between interpretations.
Following the general pattern that these judgments begin with the symbolic and end with the literal, we would see (with Talbot, a futurist) that the hail, blood and fire are symbols of Divine Wrath.  They remind us of the plagues of Egypt (less the fire).  Fire is described in two instances as representative of Christ, one in particular referring to wrath:
(Isa 10:17 NIV)  The Light of Israel will become a fire, their Holy One a flame; in a single day it will burn and consume his thorns and his briers.
Alone among the commentators I have, Lindsey insists that there is no symbolism at all in this passage -- this is John’s attempt to describe a rain of ICBMs.  I consider this a minority exception, and one of the perils of the futurist point of view.  Should the Lord tarry, who knows what weapon will be picked next?
Another minority position (Talbot) holds that trees must be considered as great men, following Daniel’s dream about Nebuchadnezzar (Daniel 4:20-22).  While this is certainly supportable in Scripture, the parallel interpretations for grass (the fleetingness of man’s life) and the earth (meaning its inhabitants) don’t seem to fit as well.  It is possible.
As usual, the futurist holds this in sequence after the rapture.  The historicist says it was fulfilled in the invasions of Alaric the Goth.