Besides the first-rate cast, majestic scenery, and excellent script, few Westerns capture the mythic history of the West better than Shane. The battle is really one between two types of society. The Rykers represent a feudal type with their land baron ownership of huge swaths of as yet barren land. I'm glad the script includes struggles they've had in taming the territory for their huge cattle-grazing purposes. It's not like they've sacrificed nothing for their dominant position. No doubt it would have been easy for the film to portray them as unadulterated bad guys.
On the other hand, The Starretts and their neighbors may be squatters on the land, but they represent a different future, one of broad settlement, farming pastures, and cooperative community. In short, they're a communal threat to the Strykers dominance. That's shown in their family gatherings, common purpose, and common desire to come together; that is, if they can resist The Strykers' effort to drive them apart. Actor Heflin's dad Starrett represents this resolve and dedication to the community dream, as well as a strong sense of personal morals, just the sort that are needed in order to lead the transition. He has the guts, but does he have the skills; that's where Shane comes in.
Of course, it's Shane and little Joey that represent the drama's appealing heart. In short, Shane amounts to the vital transition figure between the old and the new. As a gunfighter, he's a product of the open range of the Starretts, but as an exceptional man who's sampled the Starrett's family life he senses the need for constructive change and is willing to risk his life for it. Meanwhile, Joey, in a meaningful sense, represents the power of Shane's enduring norms, which Joey will no doubt carry into his own and the town's future. Ironically, however, Shane realizes that his strength is also an unintentional threat to the Starrett's cohesion as a family unit-- mom (Arthur) is attracted to him, while he's replacing dad as Joey's adult model. Thus, in the celebrated closing, Shane must ride away into an uncertain future, his contribution to civilizing the West his lasting legacy. At the same time, Joey will chase after the hope of somehow being the good man's equal in his coming years. And our last shot is Shane as he rides toward the majestic peaks he has now earned. Thus concrete events in the film transform into a spirit of the new West.
Anyway, this is my take on what I think is the film's powerful subtext embodied in characters and events. All in all, the movie was a critical hit when I was a kid, and I think it still is.