Hezekiah repeats the same idea in two ways to emphasize his point. (See: [[rc://en/ta/man/jit/figs-hyperbole]] and [[rc://en/ta/man/jit/figs-parallelism]])
"Nothing" and "not" cancel each other out to make the idea positive. This exaggeration is used for emphasis. Alternate translation: "I showed them absolutely every one of my valuable things" (See: [[rc://en/ta/man/jit/figs-doublenegatives]])