If Luke hadn’t stumbled upon it, he might have remained a moisture farmer on Tatooine for the rest of his life.
So Luke’s journey from farmer to galactic legend came full circle, from a certain point of view.
Fast-forward a little over three decades to Star Wars: The Last Jedi, even though Luke was stranded on Ahch-To, he was able help his sister one last time by Force projecting himself all the way to Ahch-To and distracting the First Order forces led by Kylo Ren so that the Resistance survivors could escape aboard the Millennium Falcon.
When we met Luke Skywalker in A New Hope, he was a simple farm boy who wanted a life of adventure and excitement, and his wish was finally granted when he came to own C-3PO and R2-D2 and accidentally discovered the message from Princess Leia Organa asking Obi-Wan Kenobi for help hidden within the latter droid.