why does Sinclair liken this Socialist meeting to a religious revival?

Jurgis focuses his attention on the speaker and is transfixed. He is surprised by how emotional he becomes at seeing the man’s eyes. “It was like coming suddenly upon some wild sight of nature, -- a mountain forest lashed by a tempest, a ship tossed about upon a stormy sea.” Jurgis is confused and disoriented, but cannot help but pay attention to the man. Jurgis is “trembling [and] smitten with wonder” by this speaker, and everyone in the hall cheers and then is silent as the man continues his speech. The man tells the crowd that a person can be “delivered from his self-created slavery” and that the systems of degradation will never again ensnare him. Jurgis stands and cheers with the crowd, overwhelmed by his emotion. He hears a voice within him, “a voice with strange intonations that rang through the chambers of the soul like the clanging of a bell.”