The final line of the First Reading from the Acts of the Apostles is, "Repent, therefore , that your sins may be wiped away." This is part of a message which Peter evidently often stated as he evangelized and spread the word about the saving grace of Jesus Christ. Penance, repentance, is an important part of our Catholic faith. One of our seven Sacraments, there is much in Church doctrine about the importance of this sacrament. The Catechism of the Catholic Church (#1424) states, "It is called the sacrament of confession, since the disclosure or confession of sins to a priest is an essential element. In a profound sense it is also a "confession," acknowledgment and praise, of the holiness of God and of His mercy toward sinful men and women."
When St. Peter was speaking and used the term "wiped away," that had more meaning to the people of his time. Imagine if sins were listed on a document in ink. In ancient times the ink had no acid content, and thus it could be "wiped away" with a damp cloth. That was the image Peter was presenting. For us, going to confession literally "wipes away" our sins.
God's forgiveness is central to the Gospel of Jesus Christ. The Sacrament of Confession (Reconciliation) means that from God's perspective it is as though our sins have never even occurred. In the Book of Hebrews the Lord declares, "I will never again remember their sins"--after repentance, that is."