This is how I always approached it:
When Belloq and the Nazis opened the Ark, the spirits that spilt and cascaded outwards were the 'transmitters' ... the in betweens if you will, between the real world and the realm of god.
However, it's obvious that mankind does not have the mental capacity to withstand the awesome power of God in any form (Kevin Smith went on to address this in 'Dogma' as well).
The power of God is thusly both so incredibly powerful and so incredibly beyond human comprehension that those who gazed upon that power had the life force blown outward (Nazi's, Belloq) sucked out (Dietrich) or...well...to be fair, Toht's demise was just really really COOL...but you get what I'm saying.
Man can't comprehend the power of God...therfore those who tried to harness that power were doomed to death.
THAT pretty much answers the OP since, as was stated, the comments were being either a bit ambiguous or a bit silly.