From the Catechism of the Catholic Church:
1420. "Those who
approach the sacrament of Penance obtain pardon from God's mercy for
the offence committed against him, and are, at the same time, reconciled
with the Church which they have wounded by their sins and which by
charity, by example and by prayer labours for their conversion."
1485.
"'On the evening of that day, the first day of the week', Jesus showed
himself to his apostles. '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" (Jn.20:19,22-23)."
1489.
"To return to communion with God after having lost it through sin
is a process born of the grace of God which is rich in mercy
and solicitous for the salvation of men. One must ask for this
precious gift for oneself and for others."
ST. PATRICK'S RC CHURCH - Waterloo
[London]
The London Parish Run by the General Delegation of the Franciscan Order of Friars Minor Conventual