Reparation, love and atonement are contained in the divine mystery so that we shall find that they expand and contract like breath the more we contemplate their meaning. At the same time as we touch the infinite, we will discover that we see the ordinary. Devotion to the Sacred Heart of Jesus as promoted by St. Margaret Mary Alacoque and St. Claude de la Columbiere certainly contained the notions of reparation, sacrificial love, and atonement. By prayer, by sacrifice and most certainly by a dialogue of love for love, a person returns to the Heart of Christ love, reparation and atonement for all who do not love Christ. Prayer makes reparation, especially when done before the Blessed Sacrament for all the outrages this Divine Heart has received from men and women, even from those who are especially consecrated to his service.
Reparation is like paying a debt, a payback, a return of something that is owed to another.
In theology it refers to a relationship one has with Christ in that you want to make up for the inadequacies of someone else's debt to God. In that respect, reparation is a participation in the redemptive action of Christ in His Passion. The person through love makes up to Christ not only for something that happened 2000 years ago on Calvary, but for the unlove which is happening this day and time. Atonement is much the same. Some might say that since Christ is God and now risen in glory, He does not need now our love and reparation.