Diary of St. Faustina is a great resource. (It's actually called
Divine Mercy in My Soul, but everyone knows it by the subtitle--good to know when looking it up on Amazon!

) It details a nun's conversations with Jesus, and focuses on the amazing power of Divine Mercy. Even just meditating on the Divine Mercy image, given to Sr. Faustina in a vision, has brought me much peace & clarity of mind. The main idea of the diary, in terms of suffering, is a simple one: Unite your sufferings with Christ's sufferings in His Passion, offer them up as prayers for the conversion of sinners, and your sufferings will be given inestimable worth.
Some paragraphs of interest:
“Suffering is a great grace; through suffering the soul becomes like the Savior; in suffering love becomes crystallized; the greater the suffering, the purer the love.” (#57, page 29)
“When I see that the burden is beyond my strength, I do not consider or analyze it or probe into it, but I run like a child to the Heart of Jesus and say only one word to Him: “You can do all things.” And then I keep silent, because I know that Jesus Himself will intervene in the matter, and as for me, instead of tormenting myself, I use that time to love Him.” (1033, page 392)
“‘I am love and Mercy Itself. There is no misery that could be a match for My mercy, neither will misery exhaust it, because as it is being granted – it increases. The soul that trusts in My mercy is most fortunate, because I Myself take care of it.’” (1273, page 459)
Though these are frightening things, the soul should not be too fearful, because God will never test us beyond what we are able to bear. On the other hand, He may never send us such sufferings, but I write this because, if it pleases the Lord to let a soul pass through such sufferings, it should not be afraid but, insofar as this depends on the soul itself, it should remain faithful to God. God will do a soul no harm, because He is Love itself, and in this unfathomable love has called it into being. However, when I was so tormented, I myself did not understand this. (Diary 106)
God made known to me what true love consists in and gave light to me about how, in practice, to give proof of it to Him. True love of God consists in carrying out God’s will. To show God our love in what we do, all our actions, even the least, must spring from our love of God. And the Lord said to me, "
My child, you please Me most by suffering. In your physical as well as your mental sufferings, My daughter, do not seek sympathy from creatures. I want the fragrance of your suffering to be pure and unadulterated. I want you to detach yourself, not only from creatures, but also from yourself. My daughter, I want to delight in the love of your heart, a pure love, virginal, unblemished, untarnished. The more you will come to love suffering, My daughter, the purer your love for Me will be". (Diary 279)
When I fell sick [probably the beginning of consumption] after my first vows and when, despite the kind and solicitous care of my Superiors and the efforts of the doctor, I felt neither better nor worse, remarks began to reach my ears which inferred that I was making believe, With that, my suffering was doubled, and this lasted for quite a long time. One day I complained to Jesus that I was being a burden to the sisters. Jesus answered me, "
You are not living for yourself but for souls, and other souls will profit from your sufferings. Your prolonged suffering will give them the light and strength to accept My will". (Diary 67)
Once the Lord said to me,
Act like a beggar who does not back away when he gets more alms [than he asked for], but offers thanks the more fervently. You too, should not back away and say that you are not worthy of receiving greater graces when I give them to you. I know you are unworthy, but rejoice all the more and take as many treasures from My Heart as you can carry, for then you will please Me more. And I will tell you one more thing — take these graces not only for yourself, but also for others; that is, encourage the souls with whom you come in contact to trust in My infinite mercy. Oh, how I love those souls who have complete confidence in Me — I will do everything for them. —
Diary, 294
