How does Primo Levi use imagery in The Drowned and the Saved?

Example of Imagery:

"An army marches by in military step, in close order, to the sound of a band; so too there must be a band in the Lager, and the march-past must be a march-past by the book, with 'eyes left' before the reviewing stand and to the sound of music. This ceremony is so necessary, so obvious, as even to prevail over the anti-Jewish legislation of the Third Reich: with paranoid sophistry, this legislation prohibited Jewish orchestras and musicians from playing the scores of Aryan composers, whom they thereby would contaminate. But in the Lagers filled with Jews there were no Aryan musicians—nor, for that matter, are there many military marches written by Jewish composers—therefore, waiving the rules of purity, Auschwitz was the only German place were Jewish musicians could, indeed were compelled to play Aryan music: necessity knows no rules."