this stands out to me because jim is clearly a man who has seen and put up with a lot, but here he loses his composure and is overwhelmed with emotion. also i think that this, combined with the fact that the last thing he sees before he can't take anymore is a little girl, really let us know more about him as a character and provide insight to the type of person jim is.

i think it's really interesting that the cavern/vaults have just been described as filled with fetid slime, and yet jim considers it to be peaceful. that says a lot about how jim has been treated above ground, and we find out later that that's probably because of his race. this is probably one of those many hints about jim's race. it also is a contrast to how the vaults quickly become a horrible thing later after the comet passes over; instead of providing peace it's like a trap.