Why was this speech so significant in changing history?

Paper details:

Read and/or watch the following and make sure to comment directly on the primary source (original historical source document):

Medieval Sourcebook: Urban II (1088-1099):
Speech at Council of Clermont, 1095, Five versions of the Speech
URLlink:http://www.fordham.edu/halsall/source/urban2-5vers.html

Answer the following question:
Why was this speech so significant in changing history?