All Mortal Sins Must Be Confessed to a Priest
"One who desires to obtain reconciliation with God and with the Church, must confess to a priest all the unconfessed grave sins he remembers after having carefully examined his conscience" (Catechism, 1493).
"All mortal sins of which penitents after a diligent self-examination are conscious must be recounted by them in confession" (Catechism, 1456).
The pattern of Scripture is to make confession to the Offended Party, and all sin is against God. "Against Thee, Thee only, have I sinned, and done this evil in Thy sight: that Thou mightest be justified when Thou speakest, and be clear when Thou judgest" (Psalm 51:4). For this reason, we are enjoined to make confession to God for the forgiveness of sins. "If we confess our sins, He is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness" (1John 1:9).
Certainly, man ought to be given confession, if he is the party that has been offended. "Moreover if thy brother shall trespass against thee, go and tell him his fault between thee and him alone: if he shall hear thee, thou hast gained thy brother" (Matthew 18:15). Confessing your sins to one another is warranted, if the offending party is to return to praying ground. "Confess your faults one to another, and pray one for another, that ye may be healed. The effectual fervent prayer of a righteous man availeth much" (James 5:16).
That phrase, "must confess to a priest" (Catechism, 1493) of Rome, viciously rips at the heart of True Christianity, for the Truly God and Yet Truly Man Christ Jesus is alone our High Priest and Mediator. "For there is one God, and One Mediator between God and men, the man Christ Jesus" (1Timothy 2:5). Any who would attempt to supplant Christ's role as our Confessor, is Against Christ-- which would make them an antichrist. "Even now are there many antichrists; whereby we know that it is the Last Time" (1John 2:18). The LORD Jesus alone is our Mediator, "Who is even at the right hand of God, Who also maketh intercession for us" (Romans 8:34). If Christ alone accepts our confession, then we are received by God-- regardless of priests that may still reject us. "To the praise of the glory of His grace, wherein He hath made us accepted in the Beloved" (Ephesians 1:6).
"One who desires to obtain reconciliation with God and with the Church" (Catechism, 1493) implies that the reconciliation is a desirable thing, but that belies the Truth. For the Earnest Believer, reconciliation with the Church of Rome is unwanted and abhorred. "Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?" (2Corinthians 6:14). Better that we make our confession to God, for only then will our peace be great. "And the peace of God, which passeth all understanding, shall keep your hearts and minds through Christ Jesus" (Philippians 4:7).