The relationship of Lennie and George in "Of Mice and Men" is thematic. For, Steinbeck's belief in the interdependence of society is a theme he explores throughout the body of his works. Steinbeck regrets that "Man's dominion has broken Nature's social order." With Lennie and George there is, at least, a brotherhood, a brotherhood which gives meaning to their lives. The aloneness of the men causes problems. Slim says of this,
I seen the guys that go around on the rnaces alone. That ain't no good. They don't have no fun. After a long time they get mean.
Crooks, the black hustler alienated from the others remarks,
A guy goes nuts if he ain't got nobody. Don't make no difference who the guy is, long's he's with you.
But, Lennie and George have each other. In a promise to Lennie's aunt, George looks out for his mentally handicapped friend while Lennie defends them if necessary. The two men struggle for a place in their Depression Era world and dream of independence, security, and a sanctuary where they will be safe. So interdependent are Lennie and George that when George must shoot Lennie to keep him from persecution, George himself loses; he loses the dream, the childlike trust of Lennie which is a sanctuary for George. Lennie provides George with someone to help him "measure the world."
At the same time that they contribute to the motifs of the novel, the characters are also symbolic. Lennie is representative of the yearning of all men and also symbolizes loyalty and trust. He obeys George when George tells him to give up the mouse in the beginning of the novella. When Curley threatens Lennie, Lennie looks at George and does not hit the man until George tells him to. George represents love and compassion. He tells Slim that it is not so strange that he and Lennie go around together. Afterall, they were born in the same place and he knew Lennie's aunt.
When his Aunt Lara died, Lennie just come along with me out workin'. Got kinda used to each other after a little while.
George even takes responsibility for Lennie; he even takes responsibilty for killing him. Before he shoots his friend, George responds to Lennie's worry that he is angry at him:
No, Lennie. I ain't mad. I never been mad, an' I ain't now. That's a thing I want ya to know.