The following is taken from Fr. Garrigou-Lagrange's Three Ages of the Interior Life.
THE NATURE OF CHARITY AND THE MARKS OF ITS PROGRESS
The signs of the progress of charity are deduced from its very nature. Scripture tells us in several places that the just man is the "friend of God." (3) St. Thomas,(4) explaining 'these words of Scripture, shows us that charity is essentially a love of friendship we should have for God because of His infinite goodness which radiates on us, vivifying us and drawing us to Himself.
Every true friendship, St. Thomas tells us, implies three qualities: it is first of all a love of benevolence by which a man wishes good to another, as to himself; in this it differs from the love of concupiscence or of covetousness, by which one desires a good for oneself, as one desires a fruit or the bread necessary to subsistence. We ought to wish our friends the good which is suitable for them, and we should wish that God may reign profoundly over minds and hearts.
Moreover, every true friendship presupposes a love of mutual benevolence; it is not sufficient that it exist on the part of one person only. The two friends should wish each other well. And the more elevated the good which they wish each other, the more noble is this friendship. It is based on virtue when friends wish each other not only what is pleasant or useful like the goods of earth and fortune, but what is virtuous - fidelity to duty, progress in the love of moral and spiritual good.
Lastly, to constitute a true friendship, this mutual love of benevolence does not suffice. We may, in fact, have benevolence for a person at a distance, whom we know only through hearsay, and that person may have the same benevolence for us; we are not, however, friends for that reason. Friendship requires in addition a community of life (convivere). It implies that people know each other, love each other, live together, spiritually at least, by the exchange of most secret thoughts and feelings. Friendship thus conceived tends to a very close union of thought, feeling, willing, prayer, sacrifice, and action.
These three characters of true friendship - the love of benevolence, mutual love, and community of life - are precisely found in the charity which unites us to God and to souls in Him.
The natural inclination which already subsists in the depths of our will, in spite of original sin, inclines us to love God, the Author of our nature, more than ourselves and above all, as in an organism the part loves the whole more than itself, as the hand exposes itself naturally to preserve the body and especially the head.(5) But this natural inclination, attenuated by original sin, cannot, without the grace which heals (gratia sanans), lead us to an efficacious love of God above all things.(6)
Far above this natural inclination, we received in baptism sanctifying grace and charity with faith and hope. And charity is precisely this love of mutual benevolence which makes us wish God, the Author of grace, the good that is suitable to Him, His supreme reign over souls, as He wishes our good for time and eternity. Such a desire is indeed a friendship based on community of life, for God has communicated to us a participation in His intimate life by giving us grace, the seed of eternal life.(7) By grace, we are "born of God," as we read in the prologue of St. John's Gospel; we resemble God as children resemble their father. And this community of life implies a permanent union, which is at times only habitual, for example, during sleep; at others, when we make an act of love of God, it is actual. Then there is truly community of life, the meeting of the paternal love of God for His child, and of the love of the child for the Father who vivifies it and blesses it. This is especially true when, by a special inspiration, the Lord inclines us to an act of infused love, which we could not make with common, actual grace. There is a spiritual communion, the prelude of the spiritual communion of heaven, which will no longer be measured by time, but by the indivisible instant of changeless eternity.
Such is indeed the friendship with God which begins on earth. Because Abraham had this love, he was called the friend of God. For the same reason the Book of Wisdom tells us that the just man lives in the divine friendship, and Christ says: "I will not now call you servants. . . but I have called you friends." By his analysis of the distinctive marks of friendship, St. Thomas only explains these divine words; he does not deduce a new truth; he explains revealed truth and enables us to penetrate it deeply.(8)
Charity, even in its least degree, makes us love God more than ourselves and more than His gifts with an efficacious love of esteem, because God is infinitely better than we and than every created gift. Efficacious love of esteem is not always felt, for example, in aridity; and at the beginning it has not yet the intensity or spontaneity that it has in the perfect, and especially in the blessed. A good Christian mother feels her love for her child, whom she holds in her arms, more than her love for God, whom she does not see; yet, if she is truly Christian, she loves the Lord with an efficacious love of esteem more than her child. For this reason, theologians distinguish commonly between appreciative love (love of esteem) and intensive love, which is generally greater for loved ones whom we see than for those who are at a distance. But, with the progress of charity, the love of esteem for God becomes more intense and is known as zeal; in heaven its impetuosity will exceed that of all our strongest affections.
Such is the nature of the virtue of charity; it is the principle of a love of God that is like the flowing of our hearts toward Him who draws us and vivifies us. Thus we ultimately find a great gratification in Him, desiring that He may reign more and more profoundly in our souls and in the souls of others. For this love of God, knowledge is not necessary; to know our heavenly Father through faith suffices. We cannot cease to love Him without beginning our own destruction, and we can cease to love Him by any mortal sin.
The efficacious love of esteem of God above all else, which may subsist in great aridity of the sensible faculties, is very much opposed to sentimentality, which is the affectation of a love one does not have.
Since such is the nature of charity, what are the indications of its progress? There are, first of all, the signs of the state of grace: 1) not to be conscious of any mortal sin; 2) not to seek earthly things, pleasures, wealth, honors; 3) to take pleasure in the presence of God, to love to think of Him, adore Him, pray to Him, thank Him, ask His pardon, talk to Him, aspire to Him. (9) To these signs must be added the following: 4) to wish to please God more than all those whom one loves; 5) to love one's neighbor effectively, in spite of the defects which are in him, as they are in us, and to love him because he is the child of God and is beloved by Him. Then one loves God in one's neighbor, and one's neighbor in God. Christ says: "By this shall all men know that you are My disciples, if you have love one for another." (10)
These signs are summed up in St. Paul's words: "Charity is patient, is kind; charity envieth not, dealeth not perversely, is not puffed up, is not ambitious, seeketh not her own, is not provoked to anger, thinketh no evil; rejoiceth not in iniquity, but rejoiceth with the truth; beareth all things, believeth all things, hopeth all things, endureth all things." (11)
Happy is the heart that loves God in this manner, without any other pleasure than that which it has in pleasing God! If the soul is faithful, it will one day taste the delights of this love and take an unequaled happiness in Him who is limitless good, the infinite plenitude of good, into which the soul may plunge and lose itself as in a spiritual ocean without ever meeting with any obstacle. Thus the just man begins to love God with a love of esteem (appreciative love) above all things, and he tends to love Him above all intensively with the ardent zeal which perseveres in aridity in the midst of trials and persecutions.
3. In the Book of Judith (8:22), Abraham is called the friend of God. Wisdom (7:27) says that the just man lives in the divine friendship. And Christ especially tells us: "I will not now call you servants. . . but I have called you friends."
4. Cf. IIa IIae, q.23, a.1.
5. Cf. St. Thomas, Ia, q.60, a.5; IIa IIae, q.26, a.3. See also St. Francis de Sales, Treatise on tbe Love of God, Bk. I, chaps. 9, 16-18.
6. Summa, Ia IIae, q.109, a.3.
7. In supernatural attrition which, with the sacrament of penance, justifies the soul, there is an initial love of benevolence, according to many theologians; but there is not yet community of life, the convivere, for there is not the state of grace.
8. St. Thomas shows that therein lies the essence of charity.
9. In Ia IIae, q. 112, a.5, St. Thomas speaks of these signs, and he adds others in the Contra Gentes, Bk. IV, chaps. 21 f. Among these last signs, St. Thomas enumerates the following: "To converse with one's friend, to delight in his presence, to be of one mind with one's friend through conformity of will, the liberty of the sons of God is in this conformity, most willingly to speak of God or to hear the word of God."
10. John 13:35.
11. Cf. I Cor. 13:4-7.