O Prophet! Tell your wives and daughters and the women of the believers to draw their cloaks closely over themselves jalābīb is the plural of jilbāb which is a wrap that covers a woman totally — in other words let them pull part of it also over their faces leaving one eye visible when they need to leave the house for something. That makes it likelier that they will be known to be free women and not be molested by being approached. In contrast slavegirls did not use to cover their faces and so the disbelievers used to pester them. And God is Forgiving of any occasion in the past when they may have neglected to cover themselves Merciful to them in His veiling them.
