This double negative is used to correct an incorrect idea that the reader might have, that the high priest cannot feel sympathy. Alternate translation: "we have a high priest who can feel sympathy ... Indeed, we have" (See: [[rc://en/ta/man/translate/figs-doublenegatives]])
This can be stated in active form. Alternate translation: "who has endured temptation in every way that we have" or "whom the devil has tempted in every way that he tempts us" (See: [[rc://en/ta/man/translate/figs-activepassive]])