When and why ritual was introduced into religion. I haven't yet found much and I'll talk to my roommate tonight about it but I found this on Wiki and found it interesting:
The purposes of rituals are varied; with religious obligations or ideals, satisfaction of spiritual or emotional needs of the practitioners, strengthening of social bonds, social and moral education, demonstration of respect or submission, stating one's affiliation, obtaining social acceptance or approval for some event—or, sometimes, just for the pleasure of the ritual itself.
http://en.wikipedia.org/wiki/RitualSince Romans were the first to bring Christianity to the masses, I'd guess ritual was introduced as a "demonstration of respect or submission, stating one's affiliation, obtaining social acceptance or approval... ." And since a lot of rituals for Christianity were borrowed from Pagan beliefs, it was a way to get Pagan's to comfortably convert to Christianity because they weren't so different from what they were already doing.
Mostly, though, I think ritual may have been introduced into religion as a way of teaching that religion to the uninformed. Sort of like that cathedral (in France, I think) that tells the story of the Bible with stained glass pictures... it was so the illiterate could learn the Bible without learning to read (which, of course, brings to question why the Church wanted to keep the masses illiterate and if the literate who translated religious texts could actually be trusted--but I'm paranoid).
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