Nicene and Post-Nicene Fathers, Ser. II, Vol. XI:
The Works of John Cassian.: Chapter XVIII.

Chapter XVIII.

Serapion: Everybody is perfectly agreed that there are eight principal faults which affect a monk. And all of them are not included in the figure of the nations for this reason, because in Deuteronomy Moses, or rather the Lord through him, was speaking to those who had already gone forth from Egypt and been set free from one most powerful nation, I mean that of the Egyptians. And we find that this figure holds good also in our case, as when we have got clear of the snares of this world we are found to be free from gluttony, i.e., the sin of the belly and palate; and like them we have a conflict against these seven remaining nations, without taking account at all of the one which has been already overcome. And the land of this nation was not given to Israel for a possession, but the command of the Lord ordained that they should at once forsake it and go forth from it. And for this cause our fasts ought to be made moderate, that there may be no need for us through excessive abstinence, which results from weakness of the flesh and infirmity, to return again to the land of Egypt, i.e., to our former greed and carnal lust which we forsook when we made our renunciation of this world. And this has happened in a figure, in those who after having gone forth into the desert of virtue again hanker after the flesh pots over which they sat in Egypt.