In order for a nation to become a repository of the oros of the whole of Israel, it must have a certain amount of holiness and impurity as well. The impurity level corresponds to the impurity that the whole of Israel bring in by their sins. The worse the sin, the higher the level of impurity. Therefore when you lose the oros to the impurity, the oros are embedded in deeper levels of impurity. In order to get them back, you must go just as deep to retrieve those lost oros. The kind of sin the whole of Israel does determines the kind of nation it will interact with, and therefore determines to which nation it will be exiled into. The impurity that the whole of Israel produces can never exceed that of the nations of the world because then those oros would be lost forever. For the whole of Israel to begin the process of redemption they must be consumed by the nation which can hold the highest level of impurity, and that nation is Amalek.