The phrase "it's beyond words" gets thrown around a lot to describe, in only a general sense, something that is just really… really hard to describe. You may have heard this said before. (Sadly, we heard this when people saw our outfit for prom, but that's another story.) What this means, though, is that there are some things in this world that are so uniquely awful that they resist our attempts to put them into language.
With Night, Elie Wiesel is doing one of the hardest things any writer can ever do: put the worst human experiences into words. It's a terrifically difficult job that he's got on his hands. In part, that difficulty helps to explain one of the calling cards of the book's writing style: sparseness. The sentences here are short, choppy, and relatively straightforward. You won't be getting lost in elaborate constructions or fancy metaphors. The horrors that Eliezer witnesses are instead told at an angle.
What do we mean? Check it out: "Behind me, an old man fell to the ground. Near him was an SS man, putting his revolver back in its holster" (3.6). Here we get just one instance of violence that our narrator witnesses. It doesn't take much to realize what's happened: the old man has been shot and killed. So, why doesn't Wiesel just write that?
The horror of the experience is such that the lack of detail is a way for the narrator (and Wiesel, too) to remove himself from the experience. Think about it. Have you ever had something really bad happen to you? Hopefully, it's nothing like what Wiesel's writing about, but even still it's no fun to go back and revel in the details. Instead, we try to shut out that kind of stuff in order to minimize its impact on our mindset.
So, the sparseness of Wiesel's writing can be attributed to that same instinct. At the same time, though, this remains a deeply personal story. Take a look at this passage:
The old man again whispered something, let out a rattle, and died amid the general indifference. His son searched him, took the bread, and began to devour it. He was not able to get very far. Two men had seen and hurled themselves upon him. Others joined in. When they withdrew, next to me were two corpses, side by side, the father and the son.
I was fifteen years old. (7.33-34)
Here we have the unthinkable murder of a father by his son. Immediately after, though, Wiesel reminds us of another tragedy: this was witnessed by a fifteen-year-old boy. While we are spared the details of exactly how the father and son die, we are nevertheless reminded of the personal impact that such a terrible event had on the narrator. So it's not like the lack of detail means that the horrors didn't impact Eliezer. In a telling way, the true damage of these experiences can be measured by what he doesn't say about them.