Lennie, throughout the novel, encourages George to repeat their "dream" of buying a plot of land and living together with both of them looking out for each other and caring for each other. The repeated refrains of this dream are that they are "going to love off the fatta the lan'". Another key part of the dream from Lennie's point of view is having lots of pet rabbits for him to look after.
This dream serves a very important purpose in the novel, as it is one of the many dreams that characters have, but in the end, it all comes to nothing. It also presents the reader with Lennie's penchant for small creatures and for petting things smaller than himself (something that we have already seen with the mouse that Lennie tries to hide from George and something which foreshadows the reason for his demise). The repeated refrain of the dream throughout the novel identifies the key theme of loneliness and offers the possibility of companionship in a very harsh setting. However, crucially, the reciting of the dream by George at the end of the novel just before he has to kill Lennie indicates the authors belief that whatever our dreams, ultimately we are people who are victims of external forces beyond our control.