The purpose of this legend is most likely to teach a lesson
related to

it’s important not to respond to the bully because doing so generally just escalates the problem.

tell a trusted adult about what is happening and save the evidence. you should also let your internet or cell phone provider know, along with the operator of the site if it is happening online.

if the bullying continues, notify the local police and consider consulting an attorney if it becomes serious.

school authorities may also become involved if it involves students on campus.

the figurative meanings of these lines are questioning the tyger's strength and beauty. the meaning contributes to the overall message of them poem because it is explaining how strong the tyger is.

now just elaborate off of that. : )