Nicene and Post-Nicene Fathers, Vol. II:
City of God: Chapter 2

Chapter 2.—Whether Among the Demons, Inferior to the Gods, There are Any Good Spirits Under Whose Guardianship the Human Soul Might Reach True Blessedness.

This book, then, ought, according to the promise made in the end of the preceding one, to contain a discussion, not of the difference which exists among the gods, who, according to the Platonists, are all good, nor of the difference between gods and demons, the former of whom they separate by a wide interval from men, while the latter are placed intermediately between the gods and men, but of the difference, since they make one, among the demons themselves.  This we shall discuss so far as it bears on our theme.  It has been the common and usual belief that some of the demons are bad, others good; and this opinon, whether it be that of the Platonists or any p. 167 other sect, must by no means be passed over in silence, lest some one suppose he ought to cultivate the good demons in order that by their mediation he may be accepted by the gods, all of whom he believes to be good, and that he may live with them after death; whereas he would thus be ensnared in the toils of wicked spirits, and would wander far from the true God, with whom alone, and in whom alone, the human soul, that is to say, the soul that is rational and intellectual, is blessed.