Stalin initiated the blockade of the city of west berlin in order to

Keep the population from fleeing to democracy (east Berlin), he promoted communism

This action was taken in order to keep away western influence away from countries of Eastern Bloc. Without the blockade, and the infamous Berlin Wall, western influence and ideals would have given revolutionary thoughts to its citizens. Not only that, the wall would have provided a line of defense against refugees. There was a huge "brain leak" during the post-war years, and it was one of the few actions to prevent it.