Street preacher

A woman regularly stands on the corner of the busy junction outside my office and preaches, sometimes with the aid of a megaphone.
She seems to get herself into a sort of frenzy, her voice and body moving to a rhythm that remains consistent.
I cannot understand whatever motivates her and I’m at a loss as to what she thinks she is achieving; her chosen pitch being so close to a six lane road that even with the megaphone the traffic drowns her message.