My opinion (which does not, of course, represent Church theology) is that the return of Jesus is through ICBMs armed with nuclear warheads, in short, global nuclear war.
I have come to bring a fire to the earth, and how I wish that it were blazing already!
Luke 12:49
See how YHWH comes in fire
His chariots like the tempest
to assuage His anger with burning,
His threats with flaming fire.
For by fire will YHWH execute jusdment,
and by His sword against all mankind.
The victims of YHWH will be many.
Isaiah 66:15-16
See! The disaster spreads
from nation to nation.
A mighty tempest rises
from the far ends of the earth.
Those slaughtered by YHWH that day will be scattered across the world from end to end.
No dirge will be raised for them; no one will gather them or bury them. They will stay lying on the surface like dung.
Jeremiah 25:32-33
So, to answer your question, neither flesh nor spirit, but, rather, fire.