Assuredly We purified them with an exclusive thought namely the remembrance of the Abode of the Hereafter in other words to always remember it and to work for it a variant reading for bi-khālisatin dhikrā’l-dār has the genitive construction bi-khālisati dhikrā’l-dār making this dhikrā al-dār ‘remembrance of the Abode’ the explicative thereof.