What is "Reparation"?

From Wikipedia ...

In the Roman Catholic tradition, an Act of Reparation is a prayer or devotion with the intent to repair the "sins of others", e.g. for the repair of the sin ofblasphemy, the sufferings of Jesus Christ or as Acts of Reparation to the Virgin Mary.[1] These prayers do not usually involve a petition for a living or deceased beneficiary, but aim to repair sins.
In his encyclical Miserentissimus Redemptor Pope Pius XI defined reparation as follows:
The creature's love should be given in return for the love of the Creator, another thing follows from this at once, namely that to the same uncreated Love, if so be it has been neglected by forgetfulness or violated by offense, some sort of compensation must be rendered for the injury, and this debt is commonly called by the name of reparation.
Pope John Paul II referred to reparation as the "unceasing effort to stand beside the endless crosses on which the Son of God continues to be crucified".
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In the encyclical Miserentissimus Redemptor Pope Pius XI called acts of reparation a duty for Roman Catholics:
We are holden to the duty of reparation and expiation by a certain more valid title of justice and of love, of justice indeed, in order that the offense offered to God by our sins may be expiated
The pontiff further emphasized, "Moreover this duty of expiation is laid upon the whole race of men"

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The need for reparation has been mentioned in some Marian apparitions. The messages of Our Lady of Akita, which were formally approved by the Holy Seein 1988 by Cardinal Joseph Ratzinger (now Pope Emeritus Benedict XVI) include the following statement attributed to the Blessed Virgin Mary:
"Many men in this world afflict the Lord. I desire souls to console Him to soften the anger of the Heavenly Father. I wish, with my Son, for souls who will repair by their suffering and their poverty for the sinners and ingrates."
Our Lady of Fatima messages have also emphasized the need for reparations. According to the child seers, Mary asked them to make sacrifices to save sinners. By this the children understood her to mean moderate acts of mortification of the flesh.