The worldly philosophers seem to have thought deeply about morality, its measurement and justifications. What should we think about these things? Do they have anything good to tell us?
We should not think that those that know not the truth know no truth at all.
The part of philosophy we call morals, or what is called by the Greeks ἠθική, in which is discussed the question concerning the chief good,—that which will leave us nothing further to seek in order to be blessed, if only we make all our actions refer to it, and seek it not for the sake of something else, but for its own sake. Therefore it is called the end, because we wish other things on account of it, but itself only for its own sake.
This beatific good, therefore, according to some, comes to a man from the body, according to others, from the mind, and, according to others, from both together. For they saw that man himself consists of soul and body; and therefore they believed that from either of these two, or from both together, their well-being must proceed, consisting in a certain final good, which could render them blessed, and to which they might refer all their actions, not requiring anything ulterior to which to refer that good itself.
This is why those who have added a third kind of good things, which they call extrinsic,—as honor, glory, wealth, and the like,—have not regarded them as part of the final good, that is, to be sought after for their own sake, but as things which are to be sought for the sake of something else, affirming that this kind of good is good to the good, and evil to the evil. Wherefore, whether they have sought the good of man from the mind or from the body, or from both together, it is still only from man they have supposed that it must be sought. But they who have sought it from the body have sought it from the inferior part of man; they who have sought it from the mind, from the superior part; and they who have sought it from both, from the whole man.
Whether therefore, they have sought it from any part, or from the whole man, still they have only sought it from man; nor have these differences, being three, given rise only to three dissentient sects of philosophers, but to many. For diverse philosophers have held diverse opinions, both concerning the good of the body, and the good of the mind, and the good of both together. Let, therefore, all these give place to those philosophers who have not affirmed that a man is blessed by the enjoyment of the body, or by the enjoyment of the mind, but by the enjoyment of God,—enjoying Him, however, not as the mind does the body or itself, or as one friend enjoys another, but as the eye enjoys light, if, indeed, we may draw any comparison between these things.
But what the nature of this comparison is, will, if God help me, be shown in another place, to the best of my ability. At present, it is sufficient to mention that Plato determined the final good to be to live according to virtue, and affirmed that he only can attain to virtue who knows and imitates God,—which knowledge and imitation are the only cause of blessedness. Therefore he did not doubt that to philosophize is to love God, whose nature is incorporeal. Whence it certainly follows that the student of wisdom, that is, the philosopher, will then become blessed when he shall have begun to enjoy God. For though he is not necessarily blessed who enjoys that which he loves (for many are miserable by loving that which ought not to be loved, and still more miserable when they enjoy it), nevertheless no one is blessed who does not enjoy that which he loves. For even they who love things which ought not to be loved do not count themselves blessed by loving merely, but by enjoying them.
Who, then, but the most miserable will deny that he is blessed, who enjoys that which he loves, and loves the true and highest good? But the true and highest good, according to Plato, is God, and therefore he would call him a philosopher who loves God; for philosophy is directed to the obtaining of the blessed life, and he who loves God is blessed in the enjoyment of God.
I hope this is fruitful to your greater understanding of these things,
(The City Of God, Book 8, Chapter 8.—That the Platonists Hold the First Rank in Moral Philosophy Also.)