The bride's great-uncle, a.k.a. the deaf-mute, a.k.a. the man in the silk hat with the Havana cigar, is probably one of the most cryptic elements of "Roof Beam." Buddy is immediately drawn to this man, even before he knows this man cannot hear or speak. Buddy finds his indifference comforting, considers him a sort of ally, and takes incredible joy in the man's appearance and general demeanor.
One interpretation is that the bride's great-uncle embodies the sort of calmness idealized by Eastern philosophies. Detachment is an important concept in many Eastern philosophies – one that Buddy discusses more fully in the short story "Teddy" (of which, remember, he claims authorship). For Buddy and Seymour, the idea is to remain socially and emotionally detached from the world around you, realizing that whatever life you're living at the time is only one of many incarnations. We suspect that Buddy recognizes and admires this detachment in the uncle, especially after reading this passage:
I glanced around at tile tiny elderly man with the unlighted cigar. The delay didn't seem to affect him. His standard of comportment for sitting in the rear seat of cars - cars in motion, cars stationary, and even, one couldn't help imagining, cars that were driven off bridges into rivers - seemed to be fixed. It was wonderfully simple. You just sat very erect, maintaining a clearance of four or five inches between your top hat and the roof, and you stared ferociously ahead at the windshield. If Death - who was out there all the time, possibly sitting on the hood - if Death stepped miraculously through the glass and came in after you, in all probability you just got up and went along with him, ferociously but quietly. Chances were, you could take your cigar with you, if it was a clear Havana. ("Roof Beam" 2.68)
Of course we have to think about the fact that the uncle can neither speak nor hear. This cannot be a coincidence in a book that is fundamentally about language and communication. Both "Roof Beam" and "Seymour" explore the impossibility of expressing truth fully or accurately through language. Scholar Ihab Hassan says it well in his article "Almost the Voice of Silence: The Later Novelettes of J. D. Salinger" – truth places an unbearable burden on language. Think about Seymour's claim that, instead of the Gettysburg Address, Lincoln should simply and silently have shaken his fist at the crowd. Or the fact that, in "Seymour," Buddy still hasn't published Seymour's poems, fearing that they will be misunderstood entirely.
This is a burden made heavier by the fact that the Glass family has their own particular language and methods of communication (such as putting quotations from Sappho on the bathroom mirror). It all adds up to Buddy not being able to tell anyone anything. In particular, Buddy has a hard time explaining things to people outside the Glass family, like Mrs. Silsburn or the Lieutenant. He tries to make them understand that Seymour, but they just don't get it.
Which is where the bride's father's uncle comes in. Because he is deaf, Buddy doesn't feel the same "burden of truth" when speaking to him. That's why he chooses to tell the uncle – and no one else – the story of how Charlotte got her stitches. No one is going to understand it anyway. (Notice that, when he tells the story, Buddy admits that Charlotte never understood why Seymour threw the stone either. Only the members of the Glass family got it.) In this way, Buddy gets to unburden himself of the truth without addressing the inherent failure of communication.
"Seymour" will pick up this theme and explore it further, starting with the opening epigraphs. We start to see that these two stories have a lot more in common than sharing characters –they also share the same problems, themes, and big ideas.