His confidence is transformed by the crowd’s response.
Scotty is described as being a "quavering husk...just moments before." This shows his lack of confidence and anxiety about being on stage. Once the crowd's enthusiasm and excitement for his performance reached him, it is described as "lifting him off his stool...unleashing something strong, charismatic, and fierce." This change in his demeanor shows his confidence grow in response the crowd.
Morrie compares himself to job in the bible.
The sentence is declarative it simply makes a statement
I believe its both but if I had to choose one I'd say
you should not chew gum in class because it's rude
Why:
It makes it look like your uninterested and not listening
If you have a cell phone yes, most students would use it for social media but it may also be used for school related topics.