Kate's motivation to return: Claire
Kate's purpose: Helping Ben reach the Others and survive

Jack's motivation to return: He is supposed to return
Jack's purpose: Unknown

Sayid's motivation to return: Unwilling passenger
Sayid's purpose: Shooting Ben to lead him to the temple

Hurley's motivation to return: Unknown
Hurley's purpose: Unknown (a great TT discussion with Miles? :))

Discuss!