Why does George speak for Lennie?

George speaks for Lennie when they are dealing with employers or potential employers because Lennie's limited intelligence would be revealed by his limited vocabulary, his monotone voice, and his general slowness in comprehending and formulating sentences. George knows that many potential employers would balk at hiring Lennie for fear that he could not understand instructions or might cause problems in other ways. Lennie is a good worker when he is told what to do. He has plenty of strength and stamina. But he can't express himself very well, and in any stressful situation he becomes hopelessly confused, as we see in several scenes in Of Mice and Men. George has been getting jobs for Lennie for as long as they have been together on the road. 

In the opening chapter, George warns Lennie not to say anything when they sign up for work at the ranch.

"Now. look--I'll give you the work tickets, but you ain't gonna say a word. You jus' stand there and don't say nothing. If he finds out what a crazy bastard you are, we won't get no job, but if he sees ya work before he hears ya talk, we're set. Ya got that?"

A little later in that same chapter, George tests Lennie.

"What you gonna say tomorrow when the boss asks you questions?"

Lennie stopped chewing and swallowed. "I . . . I ain't gonna . . . say a word."

It is obvious that Lennie would make a very poor impression on any boss if he tried to answer a few simple questions about his experience and related matters. When the two men actually do meet the boss the next day, George has to do a lot of fast thinking and fast talking to get those badly needed jobs. They ate their last three cans of beans the night before. If they don't get hired here, they will be back on the road broke, hungry, and desperate.

The boss asks Lennie:

"What can you do?"

And George quickly answers for his friend:

"He's a good skinner. He can rassle grain bags, drive a cultivator. He can do anything. Just give him a try."

Lennie creates problems for George just with the few words he says:

"Strong as a bull," he repeated.

By calling attention to himself, Lennie makes the boss suspicious and George is forced to do a lot of explaining. This scene illustrates why George has to speak for Lennie and why George is finding their relationship more and more stressful. It is hard enough for a lone bindlestiff to find a job in the middle of the Great Depression, but George is always forced to find two jobs wherever they go. George must also take a lot of abuse from employers, as he does from the boss in this scene. And this helps to explain why George, a proud, quick-tempered man, dreams of having a modest little farm of his own.