Luke hearing Obi-Wan's voice during the Trench Run. There is a wonderful realization that Luke is not alone, even with Darth Vader on his tail, and the old Jedi Knight is still around in spirit to help.
Kenobi: Remember, the Force will be with you, always.
After C-3PO spends the whole movie berating R2 and saying the whole situation is his fault, before the attack on the Death Star he just tells R2 to come back safely. "You wouldn't want my life to get boring, would you?". And when he sees R2 has been damaged, he tells Luke "Sir, if any of my circuits or gears will help, I'll gladly donate them!"