John Steinbeck wrote two novels alluding to famous stories from the Bible. The first was East of Eden which parallels the relationship between Adam and Eve's sons, Cain and Abel.
Steinbeck's second story, the novelette Of Mice and Men, alludes to the "sentence" God passes on him after Cain has murdered his brother Abel: God casts him out of his community of family and friends, where he must wander the earth for what he has done: this is God's "curse." God also places His mark upon Cain so that no one he meets will kill him for what he has done.
The parallel of Steinbeck's Of Mice and Men is that George and Lenny are also exiles, and wander through various locations during the Great Depression, looking for work, but are unable to settle down anywhere permanently and realize their dream of having a place of their own, primarily because of Lenny's unpredictable and sometimes frightening or violent behavior.
It should be mentioned that Lenny is mentally handicapped, but physically he is large and very strong. He is unaware of what he is doing. However, George is well aware of the kind of man he travels with.
George explains to others that Lenny is a cousin, and he has sworn to care for him. However, George also is deeply frustrated in that every time they settle somewhere, Lenny does something that causes the community in which they reside to hunt for them, so the men must continually move from place to place.
This is the allusion of Cain wandering, with no place to call his home, no family to welcome him in, for a crime he has committed.
And though we do not know at the novelette's beginning exactly what Lenny has done to force them on, George describes how something innocent on Lenny's part becomes serious, even dangerous, because Lenny does not understand what he is doing—his strength is also beyond his understanding of the implications that come with being able to take a life with one's bare hands.
Moving along after their last stop, George has had to take away the dead mouse Lenny has been petting in his pocket: we can assume he mistakenly killed it. When George later agrees to get Lenny a puppy, it is not long before the giant accidentally kills the puppy, and then mistakenly kills Curly's flirtatious wife.
Once again, the two men are on the run, wandering as if they are cursed: never, it seems to George, to ever be able to rest. George realizes that this time Lenny has gone too far. Throughout the story, it is evident that he feels compassion for Lenny; at the story's end, George arranges to deal with Lenny himself, rather than leaving it to the "mob" that is fast approaching.
It is at this point of the story that George describes to Lenny the homestead they will one day have; while doing so, George shoots Lenny, claiming self-defense when the others catch up.