This question already has an answer here:
Mark 1: 21-24
They went to Capernaum, and when the Sabbath came, Jesus went into the synagogue and began to teach. The people were amazed at his teaching, because he taught them as one who had authority, not as the teachers of the law. Just then a man in their synagogue who was possessed by an impure spirit cried out, “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!”
When Jesus was at Capernaum, a man who is possessed with demon came to him and spoke:
"....I know who you are—the Holy One of God!"
But he shut him up.
Mark 1:25 “Be quiet!” said Jesus sternly. “Come out of him!” The impure spirit shook the man violently and came out of him with a shriek.
And again at evening he again drove away many demons but this time he didn't allow these demons to speak at all.
Mark 1:32-34 That evening after sunset the people brought to Jesus all the sick and demon-possessed. The whole town gathered at the door, and Jesus healed many who had various diseases. He also drove out many demons, but he would not let the demons speak because they knew who he was.
- Why did Jesus stop the first demon (mentioned here) to talk and not the others mentioned later?
First demon, was so scared of Jesus and gave a testimony about Jesus(the Holy One of God) in front of everyone.
- A testimony from devil about Jesus would have make the people gathered around him to believe in Jesus more, right?