Among the complaints God has against his people in Malachi is that of wearying him with their words. He is wearied because they claim false things for him. They claim false things for him because they are self-righteous. And in their self-righteousness, they can't wait for God to appear among them and give to everyone else what they deserve.
But God tells them in very clear terms that when he appears, it will be very sudden, and they do not want to be there when that happens. For when he appears, there is no escape. He will appear either as a purifier or as a judge. Thus, we will either be purified or judged. Which category will you find yourself in on the day of his appearing?