Under this light, the only knowledge of Jesus by the demons can be explained as the implicit reference to the only people who pride themselves to know really Jesus: the Gnostics.
Just then a man in their synagogue who was possessed by an impure spirit cried out, 24 “What do you want with us, Jesus of Nazareth? Have you come to destroy us? I know who you are—the Holy One of God!”
25 “Be quiet!” said Jesus sternly. “Come out of him!” 26 The impure spirit shook the man violently and came out of him with a shriek.
25 “Be quiet!” said Jesus sternly. “Come out of him!” 26 The impure spirit shook the man violently and came out of him with a shriek.
The Messianic Secret is break only by the “demons” - Gnostics, in Mark, since only they knew what Mark was really doing, by the his judaizing Gospel: to give a new image to YHWH, by showing Jesus as the Christ of the Demiurge came to persuade the people of the essential goodness of the creator.
But then the voice of the demons is the voice of the Gnostics: “I know who you are” refers both to their knowledge of Jesus as meant by Mark (in this sense: the Messiah of the Creator) but also to their prideful knowledge of Jesus as the Son of a supreme Father (the Serpent of Genesis).
This is the reason why Jesus is accused to be in secret alliance with the “demons”, since the “demons” (the Gnostics) called Jesus the Serpent of Genesis, seen as a positive figure. But the Serpent was a negative figure for the Jews and the Judaizers.
By making silent the demons, Jesus is really destroying the gnostic heresy, even before the Great Church had the material means to do so!