Nicene and Post-Nicene Fathers, Vol. IV:
Writings in Connection with the Manichæan Controversy.: Chapter 5

Chapter 5.—Man’s Chief Good is Not the Chief Good of the Body Only, But the Chief Good of the Soul.

7.  Now if we ask what is the chief good of the body, reason obliges us to admit that it is that by means of which the body comes to be in its best state.  But of all the things which invigorate the body, there is nothing better or greater than the soul.  The chief good of the body, then, is not bodily pleasure, not absence of pain, not strength, not beauty, not swiftness, or whatever else is usually reckoned among the goods of the body, but simply the soul.  For all the things mentioned the soul supplies to the body by its presence, and, what is above them all, life.  Hence I conclude that the soul is not the chief good of man, whether we give the name of man to soul and body together, or to the soul alone.  For as according to reason, the chief good of the body is that which is better than the body, and from which the body receives vigor and life, so whether the soul itself is man, or soul and body both, we must discover whether there is anything which goes before the soul itself, in following which the soul comes to the perfection of good of which it is capable in its own kind.  If such a thing can be found, all uncertainty must be at an end, and we must pronounce this to be really and truly the chief good of man.

8.  If, again, the body is man, it must be admitted that the soul is the chief good of man.  But clearly, when we treat of morals,—when we inquire what manner of life must be held in order to obtain happiness,—it is not the body to which the precepts are addressed, it is not bodily discipline which we discuss.  In short, the observance of good customs belongs to that part of us which inquires and learns, which are the prerogatives of the soul; so, when we speak of attaining to virtue, the question does not regard the body.  But if it follows, as it does, that the body which is ruled over by a soul possessed of virtue is ruled both better and more honorably, and is in its greatest perfection in consequence of the perfection of the soul which rightfully governs it, that which gives perfection to the soul will be man’s chief good, though we call the body man.  For if my coachman, in obedience to me, feeds and drives the horses he has charge of in the most satisfactory manner, himself enjoying the more of my bounty in proportion to his good conduct, can any one deny that the good condition of the horses, as well as that of the coachman, is due to me?  So the question seems to me to be not, whether soul and body is man, or the soul only, or the body only, but what gives perfection to the soul; for when this is obtained, a man cannot but be either perfect, or at least much better than in the absence of this one thing.