The Early Church Fathers
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See that sins are forgiven through the Holy Spirit. But men make use of their ministry for the forgiveness of sins, they do not exercise the right of any power of their own. For they forgive sins not in their own name but in that of the Father and of the Son and of the Holy Spirit. They ask, the Godhead gives, the service is of man, the gift is of the Power on high.
On the Holy Spirit, Book 3, Chapter 18
If you wish to be justified, confess your sin. For a shamfaced confession of sins looses the bands of transgression. You see what God requires of you, that you remember that grace which you have received, and boast not as though you had not received it. You see by how complete a promise of remission He draws you to confession.
On Repentance, Book 2, Chapter 6
Since, however, I see that there is not yet any opportunity of coming to you, and that the summer has already begun—a season that is disturbed with continual and heavy sickness,--I think that our brethren must be dealt with; --that they who have received certificates from the martyrs, and may be assisted by their privilege with God, if they should be seized with any misfortune and peril of sickness, should, without waiting for my presence, before any presbyter who might be present, or if a presbyter should not be found and death begins to be imminent, before even a deacon, be able to make confession of their sin, that, with the imposition of hands upon them for repentance, they should come to the Lord with the peace which the martyrs have desired, by their letters to us, to be granted to them.
St. John Chrysostom
For they who inhabit the earth and make their abode there are entrusted with the administration of things which are in Heaven, and have received an authority which God has not given to angels or archangels. For has it not been said to them, ‘Whatsoever you shall bind on earth shall be bound in Heaven, and whatsoever you shall loose on earth shall be loosed in Heaven’ (Matthew 18:18)? They who rule on earth have indeed authority to bind, but only the body: whereas this binding lays hold of the soul and penetrates the heavens: and what priests do here below God ratifies above, and the Master confirms the sentence of his servants. For indeed what is it but all manner of heavenly authority which He has given them when He says, ‘Whose sins you remit they are remitted, and whose sins you retain they are retained’ (John 20:23)? What authority could be greater than this? ‘The Father has committed all judgment to the Son’ (John 5:22). But I see it all put into the hands of these men by the Son.
On the Priesthood, Book 3, Chapter 5
St. Ignatius of Antioch
For, wherever there is division or anger, God has no place. Now God forgives all who repent, so long as their repentance turns to union with God and to communion with the bishop.
Letter to the Philadelphians, Chapter 8
Catechism for Mobile Devices (SCBorromeo.org)
The Catechism of the Catholic Church (USCCB.org)
Section Two: the Seven Sacraments of the Church
Chapter Two: The Sacraments of Healing
Article 4: The Sacrament of Penance and Reconciliation
What Is This Sacrament Called?
Why a Sacrament of Reconciliation after Baptism?
The Conversion of the Baptized
The Many Forms of Penance in Christian Life
The Sacrament of Penance and Reconciliation
The Acts of the Penitent
The Minister of This Sacrament
The Effects of This Sacrament
The Celebration of the Sacrament of Penance
The Code of Canon Law (Vatican.va)
PART I. THE SACRAMENTS
TITLE IV. THE SACRAMENT OF PENANCE (Cann. 959 - 997)
CHAPTER I. THE CELEBRATION OF THE SACRAMENT
CHAPTER II. THE MINISTER OF THE SACRAMENT OF PENANCE
CHAPTER III. THE PENITENT
CHAPTER IV. INDULGENCES
The Catholic Encyclopedia (NewAdvent.org)