Saint Augustine, The City of God, Vol. II

They live in the peace of their own kind, and, when they obtain that which they seek, they live in the peace of their own kind.

CHAPTER II.

Concerning the carnal life, which is to be understood not only from the vices of the body, but also from those of the mind.

First, therefore, it must be seen what it is to live according to the flesh and what it is to live according to the spirit. For anyone who looks at what we have said at first glance, either not recalling or not paying enough attention to how the holy scriptures speak, might think that the Epicurean philosophers live according to the flesh because they placed the highest good of man in bodily pleasure, and that any others who in any way believed the good of the body to be the highest good of man, along with the entire crowd of those who do not philosophize according to some dogma but are inclined toward lust and know no joy except from the pleasures they receive through bodily senses, live according to the flesh. They might think that the Stoics, who place the highest good of man in the mind, live according to the spirit, because what is the mind of man if not a spirit? But as divine scripture speaks, both are shown to live according to the flesh. For it calls "flesh" not only the body of a terrestrial and mortal animal (just as when it says: Not all flesh is the same flesh; for there is one kind of flesh of man, another flesh of beasts, another of birds, another of fish), but it also uses the significance of this name in many other ways. Among these various modes of expression, it often calls the very man—that is, the nature of man—"flesh," using a mode of speech where the part signifies the whole, as in: By the works of the law, no flesh shall be justified. For what did it wish to be understood if not every man?