Mark 1:32-34
It is fascinating to me that our Lord, Jesus Christ, put forth the effort to mute demons. Why bother? I mean, really, what are they gonna say? There is an example of that in the first chapter of Mark. While relaxing with His friends in the evening, many people brought sick and possessed people to Him. He healed every single disease and cast out every single demon. To those cast out were forbidden to speak because "they knew Him." What does that even mean? It means many things.
First, it means that not only does He have the power and authority to cast demons out of people and animals (yes, your dog might actually be possessed; your cat definitely is) but that He has that same power and authority over them after they are cast out. As the Creator of Heaven, Earth and all of the things, both physical and spiritual, in it, He may certainly do what He chooses. Thankfully, He's not just making these rules up as He goes along. His goal is simple; to restore His creation to the way He created it. That means He wants to fix broken things. That's why He fixed me in my brokenness. Not that I'm fixed, but, closer than I was. He wants to fix you too.
Another reason that He shut their mouths was simple timing. This was very early in the public ministry of Jesus. He was still building a name for Himself and just beginning to develop a reputation as a great Teacher and a Healer. The leaders of the time were questioning who He was and how He was able to do and say the things that He did. What would not have helped that situation would be to have demons, either in people or free, speaking about His Heavenly Title and who He really was. It was just not time for that powerful truth to be revealed.
Nowhere in the Bible do we get a number of how many angels or how many demons there are. But we know that there are at least, bare minimum, 2000 demons and that is likely a very low number. Each of them were at one point in Heaven before they fell. Each of them knows that Jesus is the Son of God, the Christ. They have all seen Him in His throne and have no doubt at all of who He is. They were, and still are, as positive of that as you and I are of who the President of the USA is. It's just an unquestionable fact. But still, He does not want demons spreading the Good News. In Revelation 12 we get a glimpse of battle that has not yet happened. In it the church is victorious because of the "Blood of the Lamb and the Word of our testimonies." It is our testimonies that Christ wants. Those of His church, not His enemies. That is true in Revelation, it's true today and it was true then.
For me though, the most important reason has to do with the followers of Jesus. There weren't many things that He ever said that ONLY He could do. He was the only one that could be born of a virgin. He was the only one that could deliver His people and the rest of the world from sin and death. But as far as actions, as far as miracles, He actually told us that not only can we do the same things as Him, but we can do greater things than Him. After He had sent out the 72 they returned with incredible stories of healings and miracles and demons cast out!
If, when Jesus casts out a demon, they say that it was Him, the Christ, that did it, might it be even more difficult to believe that any of us would be able to do it? If demons say that ONLY Jesus were able to do it, how many others would try? They were silenced because more than just the Son of God can drive out demons. I can, you can. All believers can by the power of God the Father, through faith in His Son and the indwelling of the Spirit. Let's face it, if the demons were allowed to speak, all they would say would be lies. The last thing that Christ wanted was to confuse us with lies. He is the way, the TRUTH and the life.