What is the literary purpose of the interlude about the letter to the editor in Of Mice and Men?

Reading the letter is an attempt to lighten the mood in
the bunk house, but it is ineffective. Ironically, it would probably be more comfortable
if they weren't trying so hard. The fact that they do try to provide a distraction,
though, shows compassion on a ranch where such things are
rare.

The fact that the men remember Bill Tanner is
interesting, too. Most men, it seems, come and go anonymously--disappearing from
existence. The fact that he has reached a kind of celebrity status because of his letter
speaks to how lonely and disconnected these men really are. It is another subtle
reminder of the plight everyone on the ranch is faced with. What will they leave behind?
Who will know that they existed?