An excellent book that talks about this is “The Sanctifier” by Archbishop Luis Martinez.
I second this suggestion!
We were created for union with God; only in light of this truth can suffering be understood and appreciated.
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It is therefore My will that My elect shall never lay the blame on men for their trials, but that they shall rather consider My fatherly affection, which would never suffer the slightest breath of wind contrary to them if I had not in view the eternal salvation which they should receive in reward.” - Jesus to St. Gertrude
Charity unites us to God, and as St. Ignatius of Loyola says, "there is no wood better to kindle the fire of holy love than the wood of the cross, which Christ used for His own great sacrifice of boundless charity.”
It is impossible to say too much about the value of suffering. It is important to remember, however, that suffering is, in a sense, what we make of it. “The Cross is the way to Paradise, but only when it is borne willingly.” (St. Paul of the Cross)
Here are some more priceless quotes about suffering:
Jesus to St. Gertrude:
“My child, you canst do nothing more gratifying to Me than to submit patiently to all the tribulations that befall you.”
Our Lord to Bl. Battista Varani: “As you know, He has not the slightest intention of giving you paradise on earth. He wills you to be alone, quite alone, stripped of everything on the Cross whereon is consummated the holy and spiritual union of Creator and Creature.”
Jesus to Sr. Benigna Consolata: “Whenever a soul receives with faith and love any occasion of suffering, it is as if she received Me in her arms when taken down from the Cross.”
Dom Vital Lehodey: “In truth, we have need of suffering to purify, to detach, and to adorn our souls, and thereby to prepare them for union with God. We need it further to foster this union, to prevent its loss, and to bring it to perfection. The ardours of love alone would not suffice for these ends. And the reason is: because
love does not live exclusively on what it receives. Rather it lives much more on what it gives: sacrifice is always its best ailment.”
Jesus to Sr. Gertrude Mary: ‘I have My friends on earth as I have in Heaven, and My true friends are those who suffer much for love of Me. There flows out from suffering a mysterious essence that nourishes the soul, that gives it life and, so to speak, transforms it."
Fr. Paul of Moll: “If one could understand the value of an act of love for God in suffering, one would experience the greatest grief at being obliged to pass a single moment without being able to make this meritorious act."
The Almighty Father to St. Catherine of Siena (speaking of those advanced in virtue): “Suffering increases virtue, fortifies it, develops it, stirs it up. It does not move the soul, but nourishes it. No pain, no grief, can withdraw that soul from the furnace of love in which she is plunged.”
Jesus to Bl. Alexandrina da Costa: “Thousands have been saved by your terrible sufferings.”
Jesus to Sr. Jeanne Benigne Gojos: “… the slightest suffering united to that of Jesus is of more value than the pleasure to be felt in receiving the outpourings of grace.”
Jesus to Sr. Gertrude Mary: “If you meditate daily on My Passion, you will be less afraid of suffering.”
Jesus to Marie Brotel: “Love is proved by suffering: I have suffered for you, you must suffer for Me. Your sufferings have great value because they are united to Mine. I use them at My pleasure for souls, for everything is for souls.”
Jesus to St. Margaret of Cortona: “I do not wish to take away the difficulty men find in doing My will, so as not to make them lose the merit they have in suffering in order to obey Me.”
Jesus to St. Mechtilde: “My child, all the possessions in the world could not satisfy a single soul. The soul’s whole glory and salvation consist in suffering and trials. Even as a silken cloth is smooth and soft, so is every suffering and every trial sweet to the soul that truly loves God.”
Jesus to St. Veronica Giuliani: “Learn for once and all, and understand thoroughly, that suffering is the way of love. Both go together… Doubt not; fear not; I am on your side.”
Jesus to St. Crescentia: “My love, by feeding you with many sufferings, leads you to Me and makes you like unto Me… Therefore grow in My love, and walk in the way of the Cross until you come to join Me in My Kingdom.”
Jesus to St. Rose of Lima: “All My disciples must learn that affliction always accompanies grace; grace is in proportion to suffering. The number of My gifts grows with the number of trials. They must no longer be deluded as to the meaning of pain; trial is the path to perfection; by it they attain beauty of soul and the summit of grace, and the glory of the Children of God. The Cross is the true and only ladder to reach Heaven. Without the Cross this ascent is impossible.”
God to St. Mary Magdalen of Pazzi: “My child, the folly of the Cross is infinite wisdom, and the abnegation of self is singular prudence; but who understands this? Prudence is a virtue that in all things looks to the end.”
Rev. Auguste Saudrea: "One day, St. Francis of Assisi was giving way under the weight of suffering. He prayed for the grace to suffer patiently, when a voice said:
‘Francis, can you buy too dearly a jewel which enables you to gain a precious kingdom? Now this jewel is suffering, sent by God. Know that it is more valuable than all the treasures of the earth, and that you should not cast it away for the whole world, though the mountains should become solid gold and the stones diamonds and the waters balm. Then rejoice, for that is the road which leads to Heaven.’ (p. 349)
“When we truly love, we have nothing to suffer, because we find so much happiness in suffering for our Beloved.” - St. Marie–Magdalen Postel
but I love that sense of ‘nothing wasted’.