Why didn't Jesus allow demons to say he was God?

Question

After Jesus cast out demons from possessed people, he made sure that these demons didn't reveal his true identity. Why?

Example from Mar 1:24-25,34 (NIV):

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!”
...
³⁴and 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.

Answer 1

Your answer is contained within the passage you quoted;

He was not permitting the demons to speak, because they knew who He was - Mark 1:34

He didn't want the demons revealing His identity. Why? Because it wasn't time for Him to die yet. Every time the Jews began to catch on to the idea that Jesus was the Son of God, they sought to kill Him.

His desire to remain discreet until the appointed time was not limited to silencing demons;

• Jesus stretched out His hand and touched him... immediately his leprosy was cleansed. And Jesus said to him, “See that you tell no one" - Matthew 8:3-4

• Then He warned the disciples that they should tell no one that He was the Christ. - Matthew 16:20

After the transfiguration, this is what Jesus told His disciples:

• Tell the vision to no one until the Son of Man has risen from the dead. - Matthew 17:9

When the time was right, however, Jesus made His true identity clear, thereby provoking the Jews to crucify Him;

Again the high priest was questioning Him, and saying to Him, “Are You the Christ, the Son of the Blessed One?” And Jesus said, “I am"... Tearing his clothes, the high priest said, “What further need do we have of witnesses? You have heard the blasphemy; how does it seem to you?” And they all condemned Him to be deserving of death. - Mark 14:61-64

Answer 2

Because He didn't want such filthiness testifying of His divine name.

Dr. Talmage, in his classic and instructive essay Jesus the Christ, remarks as such:

On these as on other occasions we find evil spirits voicing through the mouths of their victims their knowledge that Jesus was the Christ and in all such instances the Lord silenced them with a word; for He wanted no such testimony as theirs to attest the fact of His Godship. Those spirits were of the devil's following, members of the rebellious and defeated hosts that had been cast down through the power of the very Being whose authority and power they now acknowledged in their demoniac frenzy. Together with Satan himself, their vanquished chief, they remained unembodied, for to all of them the privileges of the second or mortal estate had been denied; their remembrance of the scenes that had culminated in their expulsion from heaven was quickened by the presence of the Christ, though He stood in a body of flesh.

[Source via Google Books]

Though not exactly a worthy comparison to the magnitude of the demons' plight: if a Chevy dealership started advertising Ford products, and I was Ford, I'd ask them to stop, despite the extra publicity.

Answer 3

1. The revelation of the person of God in Jesus Christ is a most holy, sacred and defining moment in the church's history and Christian faith. It is therefore a task that inures only to God himself, at the appointed time. It is a holy revelation, and a holy appointment. To allow just anyone, much more a fallen angel, to wholly accomplish or even share such task not only usurps God's perfect plan and prerogative, but is more like throwing pearls to the pigs or the sacred to the unclean. (Matt 7:6).

2. Which brings us to the second reason: God and his work has nothing to do, and cannot intertwine howsoever, with anything that comes from the enemy. For what has light have anything to do with darkness (2 Cor 6:14). While God came to save sinners and freely associated with them (Mark 2:14-16), his work of redemption of man and revelation of his Lordship belongs to him alone. Especially that man is spiritually discerned and is only too quick to confuse what is holy from what is evil (Luke 11:14,15).