Why didn’t Jesus allow the demon he exorcised in today’s Gospel (Mark 1:21-28) to tell people who Jesus really was? Two reasons:
1. You don’t want demons to be your PR team. As the Divine Messiah of Israel, the last thing Jesus wants is demons, of all creatures, to announce to his people his true identity.
2. Exorcisms are a power struggle between exorcist and demon. Knowing someone’s name, or true identity, implies that you have some sort of power over that person. It’s a way of gaining “the upper hand”, if you will. That’s why a big part of an exorcism involves the exorcist attempting to learn the demon’s name. When the demon in Mark 1 says to Jesus, “I know who you are – the Holy One of God!”, Jesus can not let that “challenge” pass without a rebuke.
This is why Jesus essentially tells the demon, “Shut up…and get out!”
For much more on Jesus the exorcist, check this out:
“The Rite” and Jesus the Exorcist