This quotation from 1984 refers to the behavior of the citizens of Oceania during the Two Minutes Hate, when they are encouraged by the Party to vent their anger and loathing towards those deemed enemies of the state, like the mysterious Emmanuel Goldstein.
The overriding purpose of the Two Minutes Hate is to bring people together in opposition to a common enemy. In this way, any anger or frustration at the Party can be diverted towards external enemies both real and imagined. If the citizens of Oceania can be whipped up into a state of hate-filled frenzy like this, then it is much less likely that they will get any ideas about challenging the regime.
In Oceania, Emmanuel Goldstein is a living embodiment of all that is opposed to the Party and its ideology. As such, he is held up as an object of the most fanatical hatred imaginable, a truly psychotic hatred that incites those who participate in the Two Minutes Hate to feel that they're just about ready to kill, torture, and “smash faces in with a sledge hammer.” This is just how the Party wants them to be: angry, violent, and full of hatred towards its enemies.
As it turns out, it's almost certain that Emmanuel Goldstein doesn't actually exist. The likelihood is that he's nothing more than a boogeyman figure invented by the Party to provide a focus of hatred for the people of Oceania.
But as no one seems to know for sure whether or not he really does exist, the Party is able to exploit the air of mystery about him to encourage people to believe that there's a dangerous man out there with dangerous ideas who represents a real and present threat to the Party's continued rule.