Jesus has gone from Nazareth to Capernaum; in His childhood home He was unable to do any great works, as the people had their hearts set not on the Truth, but on spectacle. When He then came to Capernaum their hearts were open to the Truth, and their eyes beheld a miracle. Today the miracles continue in their midst. But then as demons are being driven out they are confessing Jesus as the Son of God, which is true, and yet Jesus rebukes them, not allowing them to speak.
Why not? Would it not only confirm what Jesus would hope all would come to say?
Jesus has this to say later about Satan and his cronies: “He was a murderer from the beginning and does not stand in truth, because there is no truth in him. When he tells a lie, he speaks in character, because he is a liar and the father of lies,” (John 8:44). Indeed Jesus is the Son of God; these demons speak the truth, but not because the truth was in them; rather they are screaming in terror, “You are the Son of God!” the same way we, in fear for our safety, might cry out “Fire!” or “Snake!” It would do the people of Capernaum no good to be evangelized by the departing demons, to be convinced of Jesus’ identity by creatures who are liars by nature: it would do them no good to start listening to demons. Therefore Jesus silences them, that they might rather be like the disciples on the mountaintop when, dazzled by the spectacle of the Transfiguration hear the voice of the Father saying, “This is my beloved Son…listen to HIM,” (Matthew 17:5).