6 There are four emotions which agitate mankind, two relating to the present, two to the future; two to good, and two to evil. There is sorrow, called in Greek λύπη, and joy, in Greek χαρά or ἡ δονή, although many translate the latter word by voluptas, pleasure; the one of which is referred to evil, the other to good. And we go too far if we rejoice over such things as we ought not, as, for example, riches, power, distinctions, the bad fortune of enemies, or their death; or, on the other hand, if we are tortured with grief on account of present evils, adversity, exile, poverty, weakness, and the death of kindred, all of which is forbidden by the Apostle.
And again, if we covet those things which we consider good, inheritance, distinctions, unvaried prosperity, bodily health, and the like, in the possession of which we rejoice and find enjoyment; or if we fear those things which we deem adverse. Now, according to the Stoics, Zeno that is to say and Chrysippus, it is possible for a perfect man to be free from these emotions; according to the Peripatetics, it is difficult and even impossible, an opinion which has the constant support of all Scripture.
Hence Josephus, the historian of the Maccabees, said that the emotions can be subdued and governed, not extirpated, and Cicero's five books of “Tusculan Disputations” are full of these discussions. According to the Apostle, the weakness of the body and spiritual hosts of wickedness in the heavenly places fight against us. And the same writer tells us that the works of the flesh and the works of the spirit are manifest, and these are contrary the one to the other, so that we do not the things that we would.
If we do not what we would, but what we would not, how can you say that a man can be without sin if he chooses? You see that neither an Apostle, nor any believer can perform what he wishes. “Love covers a multitude of sins,” not so much sins of the past as sins of the present, that we may not sin any more while the love of God abides in us. Wherefore it is said concerning the woman that was a sinner, “Her sins which are many are forgiven her, for she loved much.” And this shows us that the doing what we wish does not depend merely upon our own power, but upon the assistance which God in His mercy gives to our will.
Source: Against the Pelagians (New Advent)