It's the intention to "stand in the breach", so to speak, and offer prayer and sacrifice for one's erring brethren. This spiritual effort goes back to the beginning. Think of Job making offerings for the sins of his sons and daughters while feasting.
Ultimately, of course, there is only one great act of reparation that counts for all of us: the Passion of Christ. Our little acts of reparation are offered in union with his self-oblation and graciously accepted by Heaven.
The language used in devotional literature should not be taken too literally.
