The Role of Referees in the World Cup

The whole VAR thing I don't really get. Why do they have to wear a full kit? Do they have like Leinsman's flags as well? If England played Belgium in the final, if both teams were to win the semi-final, it'd be the first time since 1974 that a team has won the World Cup without facing a previous champion. So Germany won it in 1974, but I've never heard anyone say, well, you know what? They didn't play one of the other big teams that had won it. Who gives a flying fire?