The sacrament of Reconciliation is also known as Penance and Confession, among other names. (There is an explanation of some of these names in the Catechism's section on the sacrament of Reconciliation.) Although often called Reconciliation in common usage, the term "penance" best describes the essential interior disposition required for this sacrament. In fact, there is a virtue of penance. This is a supernatural virtue by which we are moved to detest our sins from a motive made known by faith, and with an accompanying purpose of offending God no more and of making satisfaction for our sins. In this sense the word "penance" is synonymous with "penitence" or "repentance." Before the time of Christ the virtue of penance was the only means by which people's sins could be forgiven. Even today, for those outside the Church in good faith, not possessing the sacrament of Penance, it is the only means for forgiveness of sins. Continuing the work of redemption
The sacrament of Reconciliation is a sacrament in which the priest, as the agent of God, forgives sins committed after Baptism, when the sinner is heartily sorry for them, sincerely confesses them, and is willing to make satisfaction for them. By his death on the Cross, Jesus Christ redeemed man from sin and from the consequences of his sin, especially from the eternal death that is sin's due. So it is not surprising that on the very day he rose from the dead, Jesus instituted the sacrament by which men's sins could be forgiven. A power granted by Christ
It was on Easter Sunday evening that Jesus appeared to his Apostles, gathered together in the Upper Room, where they had eaten the Last Supper. As they gaped and shrank back in a mixture of fear and dawning hope, Jesus spoke to them reassuringly. Let St. John (20:19-23) tell it:
Jesus came and stood in the midst and said to them, 'Peace be to you!' And when he had said this he showed them his hands and his side. The disciples therefore rejoiced at the sight of the Lord. He therefore said to them again, 'Peace be to you! As the Father has sent Me, I also send you.' When he had said this, he breathed upon them, and said to them, 'Receive the Holy Spirit; whose sins you shall forgive, they are forgiven them; and whose sins you shall retain, they are retained.' To paraphrase our Lord's words in more modern terms, what he said was this: As God, I have the power to forgive sin. I now entrust the use of that power to you. You will be My representatives. Whatever sins you forgive, I shall forgive. Whatever sins you do not forgive, I...