It becomes a lot more poignant with further thought. In that moment, Luke is alone in the trench. There is nobody who can help him. The one person who could come to his rescue is the last person who would, who told him it was suicide, who told him he would never risk his life on heroism, who got his reward and left without looking back. And then Han comes back.
Leia hears Han's voice on the intercom and her face lights up as she realizes he came back to help Luke and save them.
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!"
How much Threepio really cares about Artoo becomes clear when they find each other on the traders' ship. Even though the last time they were together they split up due to arguing, they're nothing but glad to see each other.
The medal awards ceremony, in particular the gentle violin melody celebrating peace and hope that follows the thunderous martial anthem of "The Force Theme." Sometimes you can't go wrong with a straightforward happy ending where the heroes get rewarded.
At the end we find out that R2 will NOT be the victim of the Heroic Sacrifice after all.
Vader actually seems to have a fairly good rapport with most of his subordinates in this one (with the obvious exception of Motti). Daine Jir feels free to question him to his face and Vader listens and even explains himself, he and his wingmen clearly work well together (even if the one guy messed up, he still tried to protect Vader from the Millennium Falcon), and in a deleted scene, Chief Bast is comfortable complaining to him about Tarkin's actions, which he considers a foolish waste of time.
When Luke realizes that the Stormtroopers must have gone to his homestead, he immediately drives home, fearing the worst. Then when he sees the farm burned, Luke starts calling for his aunt and uncle. It quickly segues into Tear Jerker but establishes that they were family.
Obi-Wan consoling Luke after discovering Owen and Beru were murdered by Stormtroopers while he was away.
Obi-Wan: There's nothing you could've done had you been there. You would have been killed too, and the droids would now be in the hands of the Empire.
Fridge Brilliance: Because Obi-Wan knows exactly what it's like to come home and find it burning, with your family dead thanks to the Empire.
The scene right after Obi-Wan saves Luke and the droids from the Tusken Raiders. Luke and Kenobi find C-3P0 with a severed arm and the droid suggests he be abandoned while the others get away. Luke's reaction is simply that of course they are not going leave their companion behind. If that does not mark Luke as a hero you can respect, nothing will in the series.
And when Threepio is lamenting about how there's no point in the others being put at risk to save him and how he's done for, Luke comfortingly replies with "No you're not, what kind of talk is that?" He's actually treating this droid — who many others could have dismissed as just a machine and abandoned to get out of danger — like a person, and it really shows what a good person Luke is.
Alternately, at that point in the movie, Luke is still focused on retrieving a newly-purchased, and probably expensive, droid so he can get to work on his farm chores, and his search has resulted in the other new droid becoming damaged. He's trying to preserve a valuable piece of equipment, and if that means he has to cajole and encourage Threepio to get him moving, then so be it.
That shows through with Luke cleaning up the droids Uncle Owen newly purchased, after all the abuse R2 and C-3P0 went through, there is something rather relieving to seeing them getting well-practised care by Luke with all the maintenance equipment needed for a thorough job.
Luke gets defensive when Han calls Obi-Wan an "old fossil," and insists he's a great man. And earlier, after the destruction of Alderaan, when Obi-Wan feels it in the force, he touches his chest as if in pain and moves to sit down quickly. Luke IMMEDIATELY switches off his light saber and rushes over to see if he's OK. It really shows their bond and how Luke not only deeply admired, but really cared about Obi-Wan.
A meta-example, overlapping with awesome; at the 1997 MTV Movie Awards, Chewbacca was given the Lifetime Achievement Award - in the form of the medal that he never got at the end of Episode IV. The really awesome part? George Lucas allowed it on one condition...that Peter Mayhew himself wear the wookiee suit. Even better, Carrie Fisher was the one who gave Chewie his medal. The ovation of the crowd was deafening.
Han spends the film belittling the Jedi and the Force, however, he says "May the Force be with you." to Luke before the Battle of Yavin.
Moments before, Han actually takes the time to offer Luke a spot on his crew, claiming that they could use a good fighter like him. Granted, Han just wanted to get as far away from the Alliance as possible, but it's still nice to finally see him respect Luke's capability, after having spent most of the film writing him off as some helpless farm boy.
At first Han doesn't get along with Luke or Leia. After their adventure on the Death Star they're best friends.
And especially after the Battle of Yavin, where they're laughing together in a big celebratory Group Hug.
A semi-Meta flub that was left in, as the joyous mood after the Death Star's destruction was so infectious that Mark Hamill accidentally called out "Carrie!" when rushing to hug Princess Leia.
It doesn't even take until after the destruction of the Death Star for Han to start taking a shine to these two kids. He offers Luke to come with him and Chewie on the Falcon instead of staying for what he thinks is the Rebels' Last Stand, and while he's frequently snarky to Luke throughout their adventure on the Death Star, it quickly slides into a big-little brother dynamic. And while Han and Leia barely have a civil word for each other from the moment they meet onward, there's a certain level of respect and admiration of each other (or at least, their ability to keep up with each others' Volleying Insults). It's what makes Han's return above so poignant and believable: he didn't come back for a payday or high-minded ideals, he came back because his new friends needed him.
Leia draping a blanket over Luke and comforting him after Obi-Wan's death. The peck on the cheek she gives him, along with some sympathetic words about Luke's regret Han won't fight, also count.
The first time Obi-Wan takes off his hood and sees R2-D2. Yeah, it's a big fat retcon, but it's easy to interpret him being coy with his phrase "I don't seem to remember owning a droid." With R2's little beep in response, you get the feeling the two of them are in on the secret while Luke and Threepio aren't.
Retcon? It's true. Anakin owned R2-D2 and C-3PO, not Obi-Wan, so he never did own a droid - or, at least, not that droid anyway.
An actually good use of being Metaphorically True, since any droids Obi-Wan did work with during the prequels would have been the property of the Jedi Order itself (likely as an extension of the Republic government), and Artoo in particular was owned by Padme/the Naboo government/Anakin. So technically, Obi-Wan never did own a droid, especially not Artoo.
Incredibly Heartwarming in Hindsight, really. Obi-Wan's spent almost 20 years on that rock as a hermit, as "Crazy Old Ben," looking after Luke from a distance and mourning his losses. Now, He's Back with R2, 3PO, a new Padawan...you can almost see how he switches from "Crazy Old Ben" to "Master and General Obi-Wan Kenobi, back in the saddle for one last adventure."
Notice the big grin he gives Luke when he says "You must learn the ways of the Force, if you're to come with me to Alderaan." In the space of an hour, both of Anakin Skywalker's children have come seeking him (Leia through her holographic recording). The Force is telling him, in no uncertain terms, that the time has come for the Jedi to rise again, at least one of the Skywalker children has proven herself a determined enemy of the Empire (Luke will come around shortly, albeit through unfortunate circumstances) and put an end to the Sith and their Empire. Obi-Wan is positively giddy.
The fact that, when Obi-Wan sacrifices himself, there's no defiance, no fear. "There is no death, only the Force," indeed. He's the Trope Namer for the Obi-Wan Moment for a reason, and it's touching to see that gentle smile he gives Luke before he passes, teaching one more lesson to both of his apprentices as he does so.
Small one but after they narrowly escape being crushed in the garbage level, Leia and Han share a hug of relief.
Meta example, but Mark Hamill recalls goofing around on set to make George Lucas laugh because the director was so stressed from the Troubled Production he looked like he was about to cry at any given moment. It's nice to see actors willing to mess up just to make their directors crack a smile.
Watching the battle of Yavin 4 after witnessing the events of Rogue One. The Death Star does get destroyed, Galen Erso's calculated design flaw WAS exploited, Rogue One's sacrifice was not in vain.
In a Meta one, there is an interview in which actor Garrick Hagon learned for the first time that his character, Biggs Darklighter, was going to be included in an previously deleted scene with Mark Hamill in the Special Edition version of the film. There is a wonderful feeling to read the delighted reaction that he is going to have an establishing dialogue scene prior to the Battle of Yavin sequence in the film after all.