Why do we need the set/push tag?

[maven apache]

Hi
I am learning the struts tag,however I can't understand why we need the
set/push/bean tag?
In my opinion,the views like jsp just need to pull data from the
Actioncontext and render them. What's the advantage of pushing new data to
context?
I am using my phone to ask this question,so I can't express more,hope you
guys know what I am talking about.^_^