Nicene and Post-Nicene Fathers, Vol. II:
City of God: Chapter 25

Chapter 25.—That Where There is No True Religion There are No True Virtues.

For though the soul may seem to rule the body admirably, and the reason the vices, if the soul and reason do not themselves obey God, as God has commanded them to serve Him, they have no proper authority over the body and the vices.  For what kind of mistress of the body and the vices can that mind be which is ignorant of the true God, and which, instead of being subject to His authority, is prostituted to the corrupting influences of the most vicious demons?  It is for this reason that the virtues which it seems to itself to possess, and by which it restrains the body and the vices that it may obtain and keep what it desires, are rather vices than virtues so long as there is no reference to God in the matter.  For although some suppose that virtues which have a reference only to themselves, and are desired only on their own account, are yet true and genuine virtues, the fact is that even then they are inflated with p. 419 pride, and are therefore to be reckoned vices rather than virtues.  For as that which gives life to the flesh is not derived from flesh, but is above it, so that which gives blessed life to man is not derived from man, but is something above him; and what I say of man is true of every celestial power and virtue whatsoever.