The following passage is taken from Fr. Garrigou-Lagrange's Three Ages of the Interior Life.
THE PRINCIPAL DEFECT OF THE WILL: SELF-LOVE
The strength of the will to move itself and to incline the other faculties to act comes from its docility to God, from its conformity to the divine will, because then, by grace, the divine strength passes into it. This is the great principle dominating this whole question.
All the meaning and the bearing of this principle are seen when we recall that, in the state of original justice, as long as the will was subject to God through love and obedience, it had the strength to command the passions completely and to reject every disorder of the sensible faculties; the passions were then totally subjected to the will vivified by charity.
Since original sin, we are born without sanctifying grace and charity, with our wills turned away from God, the supernatural last end, and weak for the accomplishment of our duties even in the natural order.
Without falling into the exaggeration of the first Protestants and the Jansenists, we must say that we are born with a will inclined to egoism, to inordinate self-love. This is called the wound of malice; it often manifests itself by a gross egoism, against which one should guard, an egoism that mingles in all man's acts. It follows that the will, which has become weak by reason of its lack of docility to God, no longer has absolute power over the sensible faculties, but only a sort of moral power or persuasion to lead them to subject themselves. Doubtless after baptism, which regenerated us by giving us sanctifying grace and charity, this wound, like the others, is in the process of healing; but it also reopens by reason of our personal sins.
The principal defect of the will is the lack of rectitude, called self-love or inordinate love of self, which forgets the love due to God and that which we should have for our neighbor. Self-love or egoism is manifestly the source of all sins. From it are born "the concupiscence of the flesh, the concupiscence of the eyes, and the pride of life." The sensible appetites, which are no longer firmly led, incline man to thoughtlessness, feverish eagerness, fruitless agitation, selfish search for all that pleases, flight from all that is painful, nonchalance, discouragement, in which he sees that his will has lost its strength, and to all sorts of bad examples.
It is clear that self-will, which is defined as that which is not conformed to the will of God, is the source of every sin. Self-will is extremely dangerous because it can corrupt everything; even what is best in one may become evil when self-will enters in, for it takes itself as its end, instead of subordinating itself to God. If the Lord perceives this will in a fast or a sacrifice, He rejects them because He sees therein a divine work accomplished through pride in order to gain approbation. Now, self-will is born of self-love or egoism; it is strong self-love that has become imperious.
On the subject of self-love or egoism, we may fall into two opposing errors: utilitarianism and quietism. Theoretical or practical utilitarianism does not see an evil in egoism, but a power that should be moderated. This doctrine, which reduces virtue to a business transaction, suppresses all morality; it reduces praiseworthy good to the useful and the delectable. This good, the object of virtue and duty, ought to be loved for itself and more than ourselves, independently of the advantages or the pleasure that may result therefrom: "Do what you ought, come what may." Practical utilitarianism leads to pride, which inclines a person to make himself the center of all who live about him; it is the manifest or hidden pride of the desire to dominate.
On the other hand, quietism condemned all interested love, even that of our eternal reward, as if there were a disorder in Christian hope, from the fact that it is less perfect than charity. Under the pretext of absolute disinterestedness, many quietists fell into spiritual sloth, which is indifferent to sanctification and salvation.
The thought of salvation and eternal beatitude is evidently very useful that we may strive to put to death inordinate love of self, which is the principal defect of our will. It is of this love that St. Augustine wrote: "Two loves have built two cities: the love of self even to the despising of God, the city of the earth; the love of God even to the despising of self, the city of God. One glorifies itself in self, and the other in the Lord. One seeks its glory from men, the other places its dearest glory in God, the witness of its conscience. The one in the pride of its glory walks with head high; the other says to its God: 'Thou art my glory, and it is Thou who dost lift up my head.' The former in its victories lets itself be conquered by its passion to dominate; the latter shows us its citizens united in charity, mutual servants, tutelary governors, obedient subjects. The former loves its own strength in its princes; the latter says to God: 'Lord, Thou art my only strength, I shall love Thee.'" One would never weary of quoting St. Augustine.
A great purification and Christian training of the will are necessary to obliterate all inordinate self-love; this result is produced in us by the progress of charity, which "unites man to God so that he lives not for himself, but for God."
Egoism is like a cancer of the will, which ravages it more and more, whereas sanctifying grace should be in it like a strong root which buries itself ever deeper in the soil in order to draw therefrom nourishing secretions and transform them into fruitful sap. We should think of the value of habitual grace, called the "grace of the virtues and the gifts," because of various proximate principles of meritorious acts springing from it. We would do well to consider that our will should possess a high degree of the virtues of justice, penance, religion, hope, and charity in order that its powers may be vastly increased.