Luke is a proxy for the audience, he doesn’t seem to know a lot about the galaxy, even about Tatooine except for his Uncle’s farm, and Tosche Station (where you can pick up some power converters), so presenting a strange weapon to him (and to the audience in the theater) and explaining where it come from, what it does, is an organic way of exposition, without it feeling like exposition to the audience. (It’s way better than say Luke noticing the lightsaber dangling from Ben’s belt and obnoxiously asking him about it)
It’s the magic of Star Wars, the 1977 movie, the necessary exposition to present this completely new universe to the audience is very natural, never feeling forced and dragging on. This is a feat that not a lot of fantasy movies are able to achieve with as near perfection as Star Wars (looking at you MCU).