If I was in World War I at about 1917, and I had to write a letter to someone, what would be included in it?

Certainly, I think that one of the elements that would
have to be conveyed is the massive amount of death that surrounded you and the entire
continent.  World War I was one of the bloodiest affairs in human history and it really
took the participants by surprise as to how bloody it actually was.  Warfighting was
seen as it really was:  Horrific.  New inventions in technology such as the machine gun
made killing more "efficient" and chemical advances in technology proved to make killing
something that happened on a larger scale.  The horror of war made it impossible to
ignore, and I would think that this has to be part of your letter at 1917.  I think that
there would be a parallel conveyance of the excitement and prospect of going to war.  So
many in Europe saw it as something to behold and with which to be enthralled as opposed
to seeing it as simply awful or a terrible affair.  In my mind, your letter might be
best to convey how much excitement there was at the start of the war effort, only to be
replaced by the despondency and despair at seeing the natural result and consequence of
war on a large scale.