Carbon Dioxide is the most important part of brewing, but why?

Ok, maybe it isn't the most important thing, but, I think it is just as important as barley, hops, water and yeast. Do you?

barley is grown, harvested and dried
hop flowers are grown, harvested and dried
barley is malted and cracked
hot water extracts fermentables
boiling begins
runnings are made into wort
hops added here and there
wort cooled
transferred to a fermenter
yeast pitched
yeast takes up residence in the wort
carbon dioxide created along with other things

What function does the carbon dioxide serve in the fermentation vessel?

Edit: To read my attempt at answering this read this.