What does it mean to collect everyone who is found in Shushan (for Esther’s fast)? Shushan was metropolis hub where people came as individuals. People were not “from” Shushan- it was not a hometown for many.  Esther wanted the Jewish people to emerge from their bubbles and fast as a community. Only as a community can we emerge from a communal crisis. 

Esther's fasts
Purim
KMTT