Isn't the Sacrament of Penance (confession) just an invention of the Church?
No. That the Sacrament of Penance was instituted by Christ can be proven in the Bible.
To Peter in Matthew 16:18, and to Peter and the other apostles in Matthew 18:18, Jesus said,
There are two applications for Jesus' promise to Peter and the other apostles. The first is that they would have the power to govern the Church in His name. The second is one fulfilled later with a special commission.
"Truly, I say to you, whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven."
In John 20:21-23 we find Jesus addressing the apostles in the upper room on the evening of the first Easter Sunday:
"'Peace be with you. as the Father has sent me, even so I send you.' And when he had said this, he breathed on them, and said to them, 'Receive the Holy Spirit. If you forgive the sins of any, they are forgiven; if you retain the sins of any, they are retained.'"
In this special commission to the apostles we find several interesting elements. The first is that Christ makes Himself clear that what He is giving the apostles is indeed a commission-mandate when He tells them that He is sending them as the Father sent Him. And what did the Father send Jesus to do? To redeem mankind, and since that redemption is now complete, it has to be applied.
The second important element is that He breathed on them. In all of human history, this is only the second time God breathed on man. The first time God had breathed on man was when He gave life to Adam. God is giving these men a new type of life here, and He is telling them they now have his power to forgive sins for those who are repentant, or to not forgive the sins of those who are not repentant.
Fourth Lateran Council
Anti-Catholic writer Loraine Boettner, author of Roman Catholicism, a book that Catholic apologist Karl Keating calls the anti-Catholic bible, writes that "auricular confession to a priest instead of to God" was invented by Pope Innocent III and the bishops of the Fourth Lateran Council in the year 1215. This is the most generally held position by those who claim the Church invented the Sacrament of Penance. Even if the Church's opponents were to completely discount the biblical references to Confession—which they do—we should expect to find no historical evidence of the sacrament's existence prior to 1215. This is not the case.
Early Christian Writers
There are many, many writings of early Christians dating to hundreds of years before the Fourth Lateran Council. St. Gregory the Great (590-604) in his homily on John 20:23 writes:
"The Apostles, therefore, have received the Holy Spirit in order to loose sinners from the bonds of their sins. God has made them partakers of His right of judgment; they are to judge in His name and in His place. The bishops are the successors of the Apostles, and, therefore, possess the same right." (Homily 26)
St. Caesarius of Arles (470-542) writes:
In a sermon on the last judgment the saint tells us…
"It is God's will that we confess our sins not only to Him but to men, and since it is impossible for us to be free of sin, we must never fail to have recourse to the remedy of Confession." (Sermon 253:1)
"to escape damnation by making a sincere Confession from the bottom of [our] hearts, and to fulfill the penance given by the priest." (Sermon 211)
St. Leo the Great (390-461) writes:
"God in His abundant mercy has provided two remedies for the sins of men; that they may gain eternal life by the grace of Baptism, and also by the remedy of Penance. Those who have violated their vows of Baptism may obtain the remission of their sins by condemning themselves; the divine goodness has so decreed that the pardon of God can only be obtained by sinners through the prayer of the priests. Jesus Christ Himself conferred upon the rulers of the Church the power of imposing canonical penance upon sinners who confess their sins, and of allowing them to receive the sacraments of Christ, after they have purified their souls by a salutary satisfaction… Every Christian, therefore, must examine his conscience, and cease deferring from day to day the hour of his conversion; he ought not expect to satisfy God's justice on his death bed. It is dangerous for a weak and ignorant man to defer his conversion to the last uncertain days of his life, when he may be able to confess and obtain priestly absolution; he ought, when he can, to merit pardon by a full satisfaction for his sins." (Epistle 108)
The great bishop St, Augustine (354-430) tells his flock to "not listen to those who deny that the Church has the power to forgive all sins." (De Agon. Christ. 3:Sermon 295.2)
St. Ambrose (340-397) declares that priests pardon all sins, not in their own name, but as "ministers and instruments of God." (De Poen., 1:2)
Paulinus of Milan (c. 395), a biographer of St. Ambrose, explicitly mentions the fact that the saint heard confessions. He writes:
"As often as anyone, in order to receive penitents, confessed his faults to him, he wept so as to compel him to weep… But he spoke of the causes of the crimes which they confessed to none but the Lord alone." (Vita Ambrosii, 39)
Origen (185-254) in his commentary on Psalm 28 writes:
"When you have eaten some indigestible food, and your stomach is filled with an excessive quantity of humor, you will suffer until you have gotten rid of it. So in like manner sinners, who hide and retain their sins within their breasts, become sick therefrom almost to death. If, however, they accuse themselves, confess their sins, and vomit forth their iniquity, they will completely drive from their souls the principle of evil. Consider carefully whom you choose to harken to your sins. Know well the character of the physician to whom you intend to relate the nature of your sickness… If he gives you advice, follow it; if he judges that your sickness is of such a nature that it should be revealed publicly in church for the edification of the brethren and your own more effective cure, do not hesitate to do what he tells you."
The great preponderance of evidence shows that Confession was not a thirteenth century invention of the Church, but that it had already been in place centuries before the Fourth Lateran Council was convoked. Still, opponents of the Church on tis issue, although they cannot explain these early writings, continue to have a problem reconciling John 20:23 to anything other than confession.
Many claim that Jesus is merely repeating His precept that we must forgive one another. But this presents a problem. It is true that Jesus taught throughout the Gospels that we are to forgive others who sin against us, but that is not what John 20:23 says. In this passage Jesus speaks only to His apostles. He gave them the power to choose whether to forgive sins. Either He was contradicting Himself in this passage from previous admonishments to forgive "seventy times seven," or He was giving the apostles a power never given man before. Since He would soon be ascending to heaven and no longer be personally present to forgive sins as He had during His ministry, He gave this power to His priesthood by way of the apostles. As Karl Keating writes: "If there is an 'invention' here, it is not the sacrament of penance, but the notion that the priestly forgiveness of sins is not to be found in the Bible or in early Christian history." (Catholicism and Fundamentalism, 189)