The word traces back to the Latin for "make ready again" ... it's the way we get ourselves and our world ready for healing.
Reparation comes from the Latin reparare, meaning to make ready again. So, when we make reparation to God, we are making our souls, indeed, the world, ready again, disposed again, to receive His grace, like tilling the soil.
But how exactly does this work? How can I do something to make up for someone else’s wrong? And in addressing the wrongs of the world, what could we do that Christ didn’t?
The answers to both questions are found in that phrase you probably glossed over in the first paragraph: the Body of Christ.
By our baptism, Christians are reborn as new creatures in Christ, and become a part of Him—He lives in us, and we live in Him. He is our head, and we are His body, as St. Paul explores beautifully in his letter to the Ephesians.
So, since we are all joined in the mysticus corpus, our actions affect each other spiritually, both for good and ill. My sins wound not only myself, but the whole body. The priest, acting in the person of Christ and representative of the whole Church, thus reconciles me both to God and to the Church.
Jesus has won our salvation for us, and we take to ourselves the effect of that atonement by Baptism and Reconciliation, where the grace merited by the Cross is available to us. Our baptism also allows us to cooperate in our sanctification, our being built up in holiness—and not just for ourselves, but for the whole Church, indeed, the whole world—by uniting our actions with the sacrifice of Christ.
We can make our own sacrifices, our own acts to repair the wounds made by sin in the world, and by virtue of being Christians, and uniting our actions to those of Christ, our acts become truly efficacious. By ourselves, we can do nothing, but we can do all things in Christ, for its by his strength that we act. (Philippians 4:13)
This helps us to understand one of the most confusing passages in the New Testament. In Colossians 1:24, St. Paul writes, “Now I rejoice in my sufferings for your sake, and in my flesh I am filling up what is lacking in the afflictions of Christ on behalf of his body, which is the church.” What could possibly be lacking in the work of Jesus? Our participation in it! St. Paul unites his own suffering to Christ’s and offers it for the Church.
St. Thomas Aquinas has a beautiful commentary on this:
I complete, that is, I add my own amount; and I do this in my flesh, that is, it is I myself who am suffering. Or, we could say that Paul was completing the sufferings that were lacking in his own flesh. for what was lacking was that, just as Christ had suffered in his own body, so he should also suffer in Paul, his member, and in similar ways in others. And Paul does this for the sake of his body, which is the Church that was to be redeemed by Christ.
In his homily on this passage, St. John Chrysostom notes that St. Paul offering his suffering “demonstrates how deeply in love he is,” born with Christ, the head, and the Church, His Body. It is acting with the love of God, agape, to take on suffering for another’s sake. Just as Christ, out of love, offered his sufferings for our sake, so we, out of love and united with Christ, can offer our suffering for the sake of others.
So, when we see our Church suffering, our love for Christ and His Bride moves us to suffer on its behalf, to offer our trials and tribulations for its sake. There are so many things we can do, from going to adoration or saying a Rosary to fasting through breakfast or asking for Mass intentions for that purpose. When we join our acts with the saving action of Christ, they become not only ours, but His, making them efficacious.
When we feel helpless in the face of evil, we must not fail to do what we can, and to remember how truly effective it is.