The other night, as we continued our way through Luke's Gospel, we were discussing Luke 9:37-45, wherein Jesus exorcises a demon from an unnamed man's only child.
One verse in particular (42) jumped out at me, not so much for what it says, but for what it doesn't say:
As he was coming forward, the demon threw him to the ground in a convulsion; but Jesus rebuked the unclean spirit, healed the boy, and returned him to his father.
What were the actual words Jesus used to exorcise the demon? St. Luke doesn't tell us.
Likewise, in the story of the Gerasene demoniac (Luke 8:26-39), Jesus doesn't tell us the actual words Jesus used to expel the demons:
A herd of many swine was feeding there on the hillside, and they pleaded with him [Jesus] to allow them to enter those swine; and he let them. The demons came out of the man and entered the swine, and the herd rushed down the steep bank into the lake and was drowned.
Now, I haven't taken the time to look at all the other Gospel stories recounting instances where Jesus exorcised demons, so I can't say whether this pattern holds true throughout such accounts, but for the aforesaid two instances, at least, I could speculate as to at least one possible explanation for why the evangelist omits the precise words Jesus uttered to expel the demons.
It goes without saying that God, being God, is all-powerful. His ability to do anything is a profound mystery that we as imperfect creatures can never quite get our head around.
One such manifestation of this amazingly awesome power God has is the ability to exorcise demons. How exactly He can do this is, by extension, a profound mystery as well.
It seems fitting, then, that the evangelist, under the guidance of the Holy Spirit, did not record the actual words Jesus used to do so. In a very real sense, our not knowing the precise words seems to better convey the mystery of how He is able to accomplish such a miracle.