The idea being conveyed in this verse is that all of these groups normally leave something behind. Thieves never take everything because they are in haste at night and so they take only that which is most valuable to them. Grape gatherers who harvest grapes in the field normally leave one or two bunches of grapes behind on the vineyard; they never take absolutely everything. All these groups (thieves, plunderers, grape gatherers) at least leave something behind. But when the Lord comes, he is going to leave nothing behind.
5 Si des voleurs, des pillards, viennent de nuit chez toi, Comme te voilà dévasté! Mais enlèvent-ils plus qu'ils ne peuvent? Si des vendangeurs viennent chez toi, Ne laissent-ils rien à grappiller?…