The rest of the chapter relates that Ezekiel himself will be a sign through the means of being struck dumb. The only words that he could speak were what God gave him to say. This was how the people would know that God was speaking.
This shows that the servant of God is a watchman sent to warn the people. What God dwells on is sin; the prophet is to warn them of their sins. There is also an element of warning them of what is coming, but this warning message also has a personal and individual aspect to it. It is not just telling the world, "The Great Tribulation is coming, and Jesus is coming not long thereafter." There is also the part of "show My people their sins." In effect, the prophet is to say, "Look, you perverts. What you are doing is not the way it should be! This is the way God has said. You should change. Repent!" This is what Ezekiel was supposed to do with the bitterness, the anger, and the astonishment that had been building inside him for seven days. God tells him, "This is how you channel that attitude and those emotions. You preach a warning message, as a watchman."
Obviously, such a job would bring him into conflict with the people; people do not like to hear such a message. They do not like to hear that things are going down the tubes, and especially that they are personally responsible. But that is basically what the watchman's message is. Nothing changes unless it begins in the individual. The individual must change! He must repent and go God's way. As more individuals do this, society will change.
However, Ezekiel has already been told that everything he says will fall on deaf ears, so he must have a forehead of flint, an undaunted, courageous spirit, to keep repeating the message until he dies.