The Three Ages of the Interior Life by Fr. Reginald Garrigou-Lagrange O.P. is one of my favorite books.

I post here an excerpt to encourage people to read the whole thing and focus on the essentials as I think that sometimes people (myself included) spend way too much time on things that are only of marginal importance and leave the most important things aside.

The whole book can be found here for free:

https://www.ecatholic2000.com/lagrange/interior1/interior.shtml

https://www.ecatholic2000.com/lagrange/interior2/interior2.shtml

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THE LOVE OF GOD DOES NOT CONSIST IN A GOLDEN MEAN

As this heading declares, the doctrine, that the supreme precept has no limit, is greatly confirmed if we consider that the end in question here is not an intermediary end, such as health, but the last end, God Himself, who is infinite good. If a sick person desires health without limitations, with greater reason we should desire the love of God, without limiting our desire to a certain degree. We do not know the degree to which God wishes to lead us and will lead us if we are faithful and generous. St. Thomas says: “Never can we love God as much as He ought to be loved, or believe and hope in Him as much as we should.”507 In contrast to the moral virtues, the theological virtues do not consist essentially in a happy mean: their object, their formal motive, their essential measure is God Himself, His infinite truth and goodness.

We are far from the aurea mediocritas of which Horace spoke. As an Epicurean, he even seriously reduced the golden mean of the moral virtues. The truly golden mean of these virtues is not only that of selfish calculation, which, without love of virtue, avoids the disadvantages of vices that are opposed to each other; the truly golden mean is already a summit, that of right reason and of virtuous good loved for itself, over and above the useful and the delectable. But this summit has not an infinite elevation; it is the reasonable rule determining the measure of our acts in the use of exterior goods and in our relations with our fellow men. For example, in the presence of certain dangers we must be courageous and even not fear death if our country is in danger; but to expose ourselves to death without a just motive would not be courage but temerity. Moreover, there are some sacrifices that our country cannot rightly require of us. Our country is not God, and consequently cannot demand that we love it above all else, sacrificing to it our Christian faith, the practice of the true religion, and our eternal salvation. Such a course of action would be an excessive love of country.

But, over and above the moral virtues, the theological virtues, which have God immediately as their object and motive, cannot essentially consist in a golden mean. We cannot love God too much, believe too greatly in Him, hope too much in Him; we can never love Him as much as He should be loved. Thus we see more clearly that the supreme precept has no limit. It asks us all ever to strive here on earth for a purer and stronger love of God.

If hope is the mean between despair and presumption, this is not because the presumptuous man hopes too greatly in God, but because he displaces the motive of hope by hoping for what God could not promise, such as pardon without true repentance. Likewise, credulity does not consist in believing too greatly in God, but in believing what is only human invention or imagination as if it were revealed by Him.508

We cannot believe too strongly in God, or hope too greatly in Him, or love Him too much. To forget, as the Epicureans do, that the rational, golden mean is already a summit, and to wish to make the theological virtues consist essentially in a golden mean as the moral virtues do, is characteristic of mediocrity or tepidity, erected into a system under pretext of moderation. Mediocrity is a mean between good and evil and, indeed, nearer evil than good. The reasonable, golden mean is already a summit, that is, moral good; the object of the theological virtues is infinite truth and goodness. This truth has at times been brought into relief by the comparison between the mediocre man and the true Christian.509

THE DUTY OF ADVANCING ON THE WAY TO ETERNITY

Finally, another reason why the precept of love has no limit is found in the fact that we are travelers on the way to eternity, and that we advance by growing in the love of God and of our neighbor. Consequently our charity ought always to grow even to the end of our journey. Not only is this a counsel, that is, something better, but an obligation. Moreover, a soul here on earth not desirous of growing in charity would offend God. The road to eternity is not made to be used as a place for rest or sleep, but rather to be traveled. For the traveler who has not yet reached the obligatory end or term of his pilgrimage, progress is commanded and not only counseled, just as a child must grow, according to the law of nature, under pain of becoming a dwarf, a deformed being.510 Now, when it is a question of advancing toward God, it is not by the movement of our bodies that we advance, but rather spiritually, by the steps of love, as St. Gregory the Great says, by growth in charity which ought to become a purer and stronger love. This is what we ought especially to ask in prayer; this is the import of the first petitions of the Our Father.

Does it follow that a person who does not yet fulfill the precept perfectly, transgresses it? Not at all; for, as St. Thomas says, “To avoid this transgression, it is enough to fulfill the law of charity to a certain extent as beginners do.

“The perfection of divine love falls entirely (universaliter) within the object of the precept; even the perfection of heaven is not excluded from it, since it is the end toward which one must tend, as Augustine says (De perfectione justitiae, chap. 8; De Spiritu et littera, chap. 36). But a person avoids the transgression of the precept by putting into practice a little love of God.

“Now, the lowest degree of the love of God consists in loving nothing more than God or contrary to God or equal with God, and he who has not this degree of perfection in no wise fulfills the commandment. There is another degree of charity which cannot be realized in this life and which consists in loving God with all our strength, in such a way that our love always tends actually toward Him. This perfection is possible only in heaven, and therefore the fact that a person does not yet possess it, entails no transgression of the commandment. And, in like manner, the fact that a person has not attained the intermediate degrees of perfection, entails no transgression, provided only that he reaches the lowest degree.”511

But evidently he who remains in this lowest degree does not fulfill the supreme commandment in all its perfection: “Thou shalt love the Lord thy God with thy whole heart and with thy whole soul and with all thy strength and with all thy mind.”

It would be an error to think that only imperfect charity is of precept, and that only the degrees of this virtue superior to the lowest degree are of counsel. They fall under the precept, if not as something to be realized immediately, at least as that toward which we must tend.512 Thus, by virtue of the law of his development, a child must grow in order to become a man, otherwise he would not remain a child, but would become a deformed dwarf. The same is true in the spiritual life.513 The law of growth has serious demands. If the divine seed, placed in us by baptism, does not develop, it runs the risk of dying, of being choked out by weeds, as we read in the parable of the sower. In the spiritual life these abnormal souls are certainly not the true mystics, but the retarded and the lukewarm.

Perfection is an end toward which all must tend, each according to his condition. This capital point of spiritual doctrine, forgotten by some modern theologians, was highlighted in 1923 by Pius XI in his encyclicalStudiorum ducem, in which he presents St. Thomas to us as the undisputed master not only of dogmatic and moral theology, but also of ascetical and mystical theology. Pius XI draws particular attention to the doctrine of the Angelic Doctor, namely, that the perfection of charity falls under the supreme precept as the end toward which every Christian must tend according to his condition in life.514

That same year Pius XI, in another encyclical, recalled the fact that St. Francis de Sales taught the same doctrine.

Three consequences, which we shall develop farther on, result from this doctrine: (1) In the way of salvation, he who does not advance, goes back. Why is this so? Because it is a law that one must always advance, under penalty of becoming a retarded soul, just as a child who does not develop as he should, becomes abnormal.(2) The progress of charity should indeed be more rapid in proportion as we approach nearer to God, who draws us more strongly. Thus the movement of a falling stone is so much the more rapid as the stone approaches the earth which attracts it.(3) Lastly, since such is the loftiness of the first precept, assuredly actual graces are progressively offered to us proportionate to the end to be attained, for God does not command the impossible. He loves us more than we think. In return, we must give Him our love.

When we have succeeded in loving Him with all our heart, even with an affective love, we must love Him with all our soul, with an effective love, with all our strength, when the hour of trial strikes for us, and finally, with all our mind, progressively freed from the fluctuations of the sensible faculties, that, henceforth spiritualized, we may become truly “adorers in spirit and in truth.”

All this doctrine shows that sanctification must not be too greatly separated from salvation, as is done by those who say: “I shall never become a saint; it is enough for me to be saved.” This statement contains an error of perspective. Progressive sanctification is, in reality, the way of salvation. In heaven there will be only saints, and, in this sense of the word, each of us must strive for sanctity

Bump

This doctrine sets a high standard and seems to make it obligatory. But how do we do it? It would require a change of life. Garrigou is telling me that I cannot be satisfied with my life if I am not perfect. But it is easy to be satisfied and I fear the changes that will put be on the way of sanctification. And Garrigou says progressive sanctification is the way of salvation. That means if I do not want to make the effort to be sanctified, I will not be saved?

Bishop Williamson has likened the spiritual life (after the Fall and Original Sin) to swimming upstream, or (my metaphor) going backwards up a down escalator.  We have the weight of Original Sin constantly tugging us downward, and if we are not struggling against that downward pull, it's going to take us down.  If I'm a fish swimming upstream and I stop struggling, I'm going to be carried away backwards by the current, or taken back to the bottom by the downward escalator if I stop walking faster than it's moving down.  So, yes, it makes sense, that if one stops making effort, that one will likely be lost.  Now as in the case of the escalator, if you're making equal effort to overcome Original Sin's downward tug, then you'll at least stay above the bottom and where you're at, rather than being pulled down to the bottom, keeping your "head above water", so to speak.  But, yeah, if you stop struggling, Original Sin is going to drag you down.

I think you're confusing ARRIVING AT perfection with STRIVING TOWARD it.  Again, with the escalator example, you may not make it to the top (in this life ... that's what Purgatory is for), but you have to keep moving, keep working, so as not to end up back at the bottom.  At some point, said escalator will stop (at your death), and then you can walk the rest of the way, but not if you've been throw off the bottom and there's a gate at the bottom locking you out after it stops.

Thank you. This is all good teaching and no doubt true. But sometimes that escalator goes down quite quickly. To keep running up is difficult. But yes, that is our vocation. And we have the examples of the saints. To get to the dark night stage is already quite advanced.