This double negative emphasizes that Naaman was the only one who was cleansed. This can also be translated in active form. Alternate translation: "the only one of them who was cleansed was Naaman" or "the only one of them whom God cleansed was Naaman" (See: [[rc://en/ta/man/jit/figs-doublenegatives]] and [[rc://en/ta/man/jit/figs-activepassive]])
A Syrian is a person from the country of Syria. The people of Syria were Gentiles, not Jews. Alternate translation: "the Gentile Naaman from Syria" (See: [[rc://en/ta/man/jit/translate-names]])