“You were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and in the Spirit of our God.” One must appreciate the magnitude of the gift God has given us in the sacraments of Christian initiation in order to grasp the degree to which sin is excluded for him who has “put on Christ.” But the apostle John also says: “If we say we have no sin, we deceive ourselves, and truth is not in us.” And the Lord himself taught us to pray: “Forgive us our trespasses,” linking our forgiveness of one another’s offenses to the forgiveness our sins that God will grant us. (CCC 1425)
“When Christ’s faithful strive to confess all the sins that they can remember, they undoubtedly place all of them before the divine mercy of pardon, but those who fail to do so and knowingly withhold some, place nothing before the divine goodness for remission through the mediation of the priest, “. . .for if the sick person is too ashamed to show his wound to the doctor, the medicine cannot heal what it does not know.”
Council of Trent (1551): DS 1680 (ND 1626); cf. St. Jerome, In Eccl. 10,11: PL 23:1096