From The Three Ages of the Interior Life, Ch. 3:
THE INFUSED MORAL VIRTUES
Are the acquired moral virtues we have just spoken of sufficient, under the influence of charity, to constitute the spiritual organism of the virtues in a Christian? Must we receive infused moral virtues?
In conformity with tradition and with a decision of Pope Clement V at the Council of Vienne,(5) the Catechism of the Council of Trent (Part II, On baptism and its effects), answers: "The grace (sanctifying), which baptism confers, is accompanied by the glorious cortege of all the virtues, which, by a special gift of God, penetrate the soul simultaneously with it." This gift is an admirable effect of the Savior's passion which is applied to us by the sacrament of regeneration.
Moreover, in this bestowal of the infused moral virtues, there is a lofty fitness that has been well set forth by St. Thomas.(6) The means, he observes, must be proportioned to the end. By the infused theological virtues we are raised and directed toward the supernatural last end. Hence it is highly fitting that we should be raised and directed by the infused moral virtues in regard to supernatural means capable of leading us to our supernatural end.
God provides for our needs not less in the order of grace than in that of nature. Therefore, since in the order of nature He has given us the capacity to succeed in practicing the acquired moral virtues, it is highly fitting that in the order of grace He should give us infused moral virtues.
The acquired moral virtues do not suffice in a Christian to make him will, as he ought, the supernatural means ordained to eternal life. St. Thomas says, in fact, that there is an essential difference between the acquired temperance described by pagan moralists, and the Christian temperance spoken of in the Gospel. (7) The difference is analogous to that of an octave between two musical notes of the same name, separated by a complete scale. We often distinguish between philosophical temperance and Christian temperance, or again between the philosophical poverty of Crates' and the evangelical poverty of the disciples of Christ.
As St. Thomas remarks,(8) acquired temperance has a rule and formal object different from those of infused temperance. Acquired temperance keeps a just medium in the matter of food in order that we may live reasonably, that we may not injure our health or the exercise of our reason. Infused temperance, on the contrary, keeps a superior happy mean in the use of food in order that we may live in a Christian manner, as children of God, en route to the wholly supernatural life of eternity. Infused temperance thus implies a more severe mortification than is implied by acquired temperance; it requires, as St. Paul says, that man chastise his body and bring it into subjection,(9) that he may become not only a virtuous citizen of society on earth, but one of the "fellow citizens with the saints, and the domestics of God." (10)
The same difference exists between the acquired virtue of religion, which ought to render to God, the Author of nature, the worship due Him, and the infused virtue of religion, which offers to God, the Author of grace, the essentially supernatural sacrifice of the Mass, which perpetuates in substance that of the cross. Between these two virtues of the same name, there is even more than the difference of an octave; there is a difference of orders, so that the acquired virtue of religion or that of temperance could grow forever by the repetition of acts without ever attaining the dignity of the slightest degree of the infused virtue of the same name. The tonality is entirely different; the spirit animating the word is no longer the same. In the case of the acquired virtue, the spirit is simply that of right reason; in the infused virtue, the spirit is that of faith which comes from God through grace.
These two formal objects and two motives of action differ greatly. Acquired prudence is ignorant of the supernatural motives of action; infused prudence knows them. Proceeding not from reason alone, but from reason illumined by infused faith, it knows the infinite elevation of our supernatural last end, God seen face to face. It knows, consequently, the gravity of mortal sin, the value of sanctifying grace and of the actual graces we must ask for every day in order to persevere, and the value of the sacraments that are to be received. Acquired prudence is ignorant of all of this, because this matter belongs to an essentially supernatural order.
What a difference there is between the philosophical modesty described by Aristotle and Christian humility! The latter presupposes the knowledge of two dogmas: that of creation ex nihilo, and that of the necessity of actual grace for taking the slightest step forward in the way of salvation. What a distance there is also between the virginity of the vestal virgin, whose duty it was to keep up the sacred fire, and that of the Christian virgin who consecrates her body and heart to God that she may follow our Lord Jesus Christ more perfectly!
These infused moral virtues are Christian prudence, justice, fortitude, temperance, and those which accompany them, such as meekness and humility. They are connected with charity in this sense, that charity, which sets us aright in regard to our supernatural last end, cannot exist without them, without this multiple rectification in regard to the supernatural means of salvation.(11) Moreover, he who loses charity by a mortal sin, loses the infused moral virtues; because, by turning away from the supernatural end, he loses infused rectification in regard to the means proportioned to this end. But it does not follow that he loses faith and hope, or that he loses the acquired virtues; the latter, however, cease to be stable and connected in him. In fact, a man who is in the state of mortal sin loves himself more than he does God and tends through egoism to fail in his duties even in the natural order.