on Confession

Augustine of Hippo Sermon to Catechumens on the Creed par 15 [354-430 AD]
"When you shall have been baptized, keep to a good life in the commandments of God so that you may preserve your baptism to the very end. I do not tell you that you will live here without sin, but they are venial sins which this life is never without. Baptism was instituted for all sins. For light sins, without which we cannot live, prayer was instituted. . . . But do not commit those sins on account of which you would have to be separated from the body of Christ. Perish the thought! For those whom you see doing penance have committed crimes, either adultery or some other enormities. That is why they are doing penance. If their sins were light, daily prayer would suffice to blot them out. . . . In the Church, therefore, there are three ways in which sins are forgiven: in baptisms, in prayer, and in the greater humility of penance"
Augustine of Hippo Enchiridion Ch 83 [354-430 AD]
Now the man who, not believing that sins are remitted in the Church, despises this great gift of God's mercy, anti persists to the last day of his life in his obstinacy of heart, is guilty of the unpardonable sin against the Holy Ghost
Augustine of Hippo Enchiridion Ch 65 [354-430 AD]
and outside the Church sins are not remitted. For the Church alone has received the pledge of the Holy Spirit, without which there is no remission of sins--such, at least, as brings the pardoned to eternal life.
Augustine Reply to Faustus the Manichean Book 22 pa 29 (354-430 ad)
But if this unbridled course ends in plunging the man into such a depth of evil habits that he supposes that there will be no punishment of his sinful passions, and so refuses the wholesome discipline of confession and repentance by which he might be rescued; or, from a still worse insensibility, justifies his own indulgences in profane opposition to the eternal law of Providence; and if he dies in this state, that unerring law sentences him now not to correction, but to damnation.
Augustine Exposition on Psalm 102 par 20 (354-430 ad)
When is he loosed, and by whom is he loosed? "Whatsoever thou shall
loose on earth," He saith, "shall be loosed in Heaven.
Forgiveness of sins may justly be granted by the Church
Augustine Exposition on Psalm 94 par 11 (354-430 ad)
In the words then, Who is the proud? He who doth not by confession of his sins do penance, that he may be healed through his humility.
Augustine Sermon 49 par 9 (354-430 ad)
"If men do not forgive sins, then that is false which Christ saith, 'Whatsoever ye shall loose on earth, shall be loosed in heaven also.'" But thou dost not know why this is said, and in what sense this is said. The Lord was about to give to men the Holy Spirit, and He wished it to be understood that sins are forgiven to His faithful by His Holy Spirit, and not by men's deserts. For what art thou, O man, but an invalid who hast need of healing. Wouldest thou make thyself my physician? Together with me, seek the Physician. For that the Lord might show this more plainly, that sins are forgiven by the Holy Spirit, which He hath given to His faithful ones, and not by men's deserts, after He had risen from the dead, He saith in a certain place, "Receive ye the Holy Ghost;" and when He had said, sins ye remit, they are remitted unto them;" that is, the Spirit remits them, not ye. Now the Spirit is God. God therefore remits, not ye. But what are ye in regard to the Spirit? "Know ye not that ye are the temple of God, and the Spirit of God dwelleth in you?" And again, "Know ye not that your bodies are the temples of the Holy Ghost which is in you, which ye have of God?" So then God dwelleth in His holy temple, that is in His holy faithful ones, in His Church; by them doth He remit sins; because they are living temples