Bansky secret helped make him famous.
Bansky uses the walls of building for his painting.
The soilder is trying to convoy that is sweet sorrow dying for their nation.
The reason the author may have chosen short sentences is to show Elie’s racing thoughts of depression, anxiety, and struggle with his pessimistic thoughts about possibly being chosen for the next (i think it’s called selection) selection to the ovens.
I hope this helps I tried to remember when I read this