Why the need to Invoke the Demon's Nemesis (Saint) in the Rite of Exorcism?

Often, I get a good (and often standard) question about how things work in the realm of spiritual warfare.  While they often have to do with exorcisms, the work of an exorcist in casting out demons is very much related to our own spiritual work in resisting diabolical attacks, whether ordinary or extraordinary. Q:  Why does the exorcist need to invoke the name of the demon's nemesis (Saint) if