Here "There was nothing ... did not show them" is an exaggeration used for emphasis. It means Hezekiah showed them all of his most valuable things. This can be stated in positive form. AT: "Hezekiah showed him absolutely everything valuable in his house and in all his kingdom" (See: [[rc://en/ta/man/translate/figs-doublenegatives]] and [[rc://en/ta/man/translate/figs-hyperbole]])