Youcat commented through CCC – Question n. 317.

YOUCAT Question n. 317 - How can a person be delivered from a serious sin and reunited with God?

(Youcat answer)  In order to heal the break with God that is caused by a serious sin, a Catholic Christian must be reconciled with God through confession.

A deepening through CCC

(CCC 1856) Mortal sin, by attacking the vital principle within us - that is, charity - necessitates a new initiative of God's mercy and a conversion of heart which is normally accomplished within the setting of the sacrament of reconciliation: When the will sets itself upon something that is of its nature incompatible with the charity that orients man toward his ultimate end, then the sin is mortal by its very object…  whether it contradicts the love of God, such as blasphemy or perjury, or the love of neighbor, such as homicide or adultery.... But when the sinner's will is set upon something that of its nature involves a disorder, but is not opposed to the love of God and neighbor, such as thoughtless chatter or immoderate laughter and the like, such sins are venial (St. Thomas Aquinas, STh I-II, 88, 2, corp. art.).     

Reflecting and meditating 

(CCC Comment)

(CCC 1446) Christ instituted the sacrament of Penance for all sinful members of his Church: above all for those who, since Baptism, have fallen into grave sin, and have thus lost their baptismal grace and wounded ecclesial communion. It is to them that the sacrament of Penance offers a new possibility to convert and to recover the grace of justification. The Fathers of the Church present this sacrament as "the second plank [of salvation] after the shipwreck which is the loss of grace" (Tertullian, De Paenit. 4, 2: PL 1, 1343; cf. Council of Trent (1547): DS 1542).

(The next question is: What are vices?)