Satisfaction
Satisfaction is the third act of the penitent in the sacrament of penance: to repair the disorder that sin caused, by accomplishing the penalty the priest indicates, prayer, fasting or good work. It is what is commonly called the penance given at the confessional.
A penalty that remains after the pardon
When sin is forgiven, the fault is erased and the eternal penalty remitted. There yet often remains a temporal penalty, a debt to be acquitted. Scripture shows it in the history of David: his sin confessed, the prophet Nathan announces to him the pardon, then a penalty that subsists. “The Lord has forgiven your sin; you will not die.” 2 Samuel 12:13 And yet the child born of the fault will die: the pardon of the fault has not erased every consequence.
To repair is to heal
This reparation does not seek to sway a demanding God, for forgiveness is given freely. It heals the sinner of the attachment that sin has left in him, and redresses the wrong committed. When Zacchaeus converts, he does not stop at regret: he repairs. “If I have wronged anyone, I restore to him fourfold.” Luke 19:8 Prayer, fasting and almsgiving are the traditional ways of this reparation; when a precise wrong has been done to the neighbor, satisfaction asks first to redress it.
Grafted onto the Cross
Our satisfactions have no value by themselves alone: they receive it from the one satisfaction of Christ, who repaired on the Cross what no man could repair. United to his, our accepted penalties become fruitful. What has not been repaired before death will be in purgatory; and the Church, drawing on the treasury of the merits of Christ, can remit part of it by indulgences.