I would have to say

Getting to know Uncle Owen and Aunt Beru and then seeing their dead burned bodies through Luke’s eyes. Them dying pushes Luke towards his destiny.
The twin sunset I feel how Luke yearns for something more than just his uncle’s farm. He has to postpone his dreams for another year.
Vader and Kenobi fight. Luke witnesses his mentor killed before his eyes.
Luke taking out the Death Star and Han Solo showing up to help. After suffering 2 family losses, a teacher, and his childhood friend Biggs, Luke uses the force to beat the odds and successfully destroy a planet killer.

I have four, not three.