One element is the framing structure of the play. It opens with a group of workers deciding whether to strike as they wait for Lefty. Several of them introduce a story that is then enacted as a theatrical vignette. This feeds the collectivist attitude of the play - we all have stories to tell, and by telling them do we realize we are all bound by the same oppressions that we, as proletariat, could have control over if we strike. Each story told helps to further this idea and prepare to characters to be angry enough to strike when they hear Lefty has died. Another element is the antipathy for communism, or "redness." Even within the meeting of workers, the union leader and his gunmen keep them in control by use of the insult "red," and the use of the gunmen makes it a vague threat. The play, with its stories slowly building up a fortitude of indignation in the characters gathered, traces their transition to accepting communism not as something they should avoid, but embrace. You can find plenty of supporting examples for these trends through the particular scenes.