Thank you Wordwind and Angel!

While it seems as though the spire of a church represents the aspirations of humankind to be with God, a brief search at Merriam-Webster's webpage suggests that the word is related to an archaic word for a blade of grass. Presumably the tall, narrow shape of the spire on a church suggested a blade of grass to whoever coined the name.

From http://www.m-w.com/home.htm

Main Entry: spire
Pronunciation: 'spIr
Function: noun
Etymology: Middle English, from Old English spIr; akin to Middle Dutch spier blade of grass
Date: before 12th century
1 : a slender tapering blade or stalk (as of grass)
2 : the upper tapering part of something (as a tree or antler) : PINNACLE
3 a : a tapering roof or analogous pyramidal construction surmounting a tower b : STEEPLE

I really love these etymological discussions. Maybe I should get myself an OED. They are a bit pricey though, aren't they?