This moment in Of Mice and Men is significant to the eye of the beholder, and perhaps Steinbeck wanted to cause just that effect on the reader. If you have ever been in a situation as desperate as that of the farmhands, you will certainly appreciate Whit's emotional state. If you have not, you may find Whit unsophisticated and overly excited over nothing. It depends on how you read it. To most, however, this is indeed a significant moment for Whit for several reasons.
Whit, a young farmhand, feels very excited to show the men this magazine that he has just found out about. Naturally, he wants Slim, the most promising of the farmhands, to read aloud the information Whit pointed at.
What Slim proceeds to read is a letter to the editor of the magazine, which reads:
’Dear Editor,’” [..] “’I read your mag for six years and I think it is the best on the market. I like stories by Peter Rand. I think he is a whing-ding. Give us more like the Dark Rider. I don’t write many letters. Just thought I would tell you I think your mag is the best dime’s worth I ever spent.’”
While Slim questioned more than once what was the purpose of reading that, Whit was way too excited to announce that the person who wrote the letter to the editor used to be a farmhand right there at that ranch, and that he worked alongside him.
Of noteworthy mention are two things. First, that Whit does not relinquish control of the magazine. He keeps holding it at all times and does not let go. Second, that Whit's excitement goes beyond recognizing someone's name in a magazine; after all, even Slim had to ask him whether he was absolutely certain that this is the same "Bill" that he used to know.
Here is what makes the entire event more significant, especially to whose who have been in a situation like the farmhands: hopeless, isolated, lonely. It is the fact that he is excited to announce that Bill accomplished a mission. In other words, he is cathartically and vicariously experiencing some degree of success at witnessing someone that used to be right there where he still is now having some form of accomplishment, albeit one that is quite simple.
“I know it. Bill and me was in here one day. Bill had one of them books that just come. He was lookin’ in it and he says, ‘I wrote a letter. Wonder if they put it in the book!’ But it wasn’t there. Bill says, ‘Maybe they’re savin’ it for later.’ An’ that’s just what they done. There it is.”
These words are not just excitement and wonder. They embody hope, the wishful thinking that there is a way out of the ranch; a way to leave that place whether in body or in spirit. This person, Bill, had a wish come true. Perhaps there is also a glint of hope for Whit that one of his own wishes will also come to be. That magazine was a temporary mental ticket out of his current situation; it was a palpable token that did represent possibilities. This is why he neither allow anyone else to touch it, nor could hide his obvious excitement about this event.