Sum up what Slim says about the relationship between knowledge and kindness in Of Mice and Men.

Sim says that a person doesn’t have to be smart to be kind.

Slim and George have a conversation about Lennie when Slim mentions that it is unusual for two guys to stick together.  Most of the ranch hands are loners.  George explains that Lennie is not smart, but is still good.  He gives examples of the abuses he has heaped on Lennie that Lennie just took in stride.  Lennie cares about George, and would never hurt him.

Slim comments that brains are not needed to be a good person.

"He's a nice fella," said Slim. "Guy don't need no sense to be a nice fella. Seems to me sometimes it jus' works the other way around. Take a real smart guy and he ain't hardly ever a nice fella." (Ch. 3)

Lennie may be mentally challenged, but he is kind and a good friend in his own way.  He would never do anything against anyone.  He is childlike in his demeanor, and while he sometimes accidentally hurts people or animals, it is only because he doesn’t know his own strength.

George agrees, commenting that being lonely can turn a person mean.  He and Lennie have each other, and it helps them face the world.  George tells Slim that Lennie can be a nuisance.

"'Course he ain't mean. But he gets in trouble alla time because he's so God damn dumb. Like what happened in Weed-" (Ch. 3)

Slim seems a bit jealous of the relationship between George and Lennie.  He too is a genuinely good guy, and well-respected on the ranch.  George opens up to him, even though he normally is very protective of Lennie and doesn’t tell people about him.  Slim’s disarming nature makes it easy to talk to him.

Both the comments are Lennie's niceness and the story about what happened in Weed foreshadow Lennie's trouble with Curley's wife.  Lennie is a nice guy, so he didn't mean to kill her.  He likes soft things though, and this can be disastrous.  Lennie doesn't learn from his mistakes.