Jesus entrusted the ministry of reconciliation to the Church.  The Sacrament of Penance is God's gift to us so that any sin committed after Baptism can be forgiven.  In confession, we have the opportunity to repent and recover the grace of friendship with God. It is a holy moment in which we place ourselves in his presence and honestly acknowledge our sins, especially mortal sins.  With absolution, we are reconciled to God and the Church. The Sacrament helps us stay close to the truth that we cannot live without God. "In him we live and move and have our being" (Acts 17:28). 

The Catechism of the Catholic Church says this about the Sacrament of Reconciliation: 
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."
1447 Over the centuries the concrete form in which the Church has exercised this power received from the Lord has varied considerably. During the first centuries, the reconciliation of Christians who had committed particularly grave sins after their Baptism (for example, idolatry, murder, or adultery) was tied to a very rigorous discipline, according to which penitents had to do public penance for their sins, often for years, before receiving reconciliation. To this "order of penitents" (which concerned only certain grave sins), one was only rarely admitted and in certain regions only once in a lifetime. During the seventh century Irish missionaries, inspired by the Eastern monastic tradition, took to continental Europe the "private" practice of penance, which does not require public and prolonged completion of penitential works before reconciliation with the Church. From that time on, the sacrament has been performed in secret between penitent and priest. This new practice envisioned the possibility of repetition and so opened the way to a regular frequenting of this sacrament. It allowed the forgiveness of grave sins and venial sins to be integrated into one sacramental celebration. In its main lines, this is the form of penance that the Church has practiced down to our day.
1448 Beneath the changes in discipline and celebration that this sacrament has undergone over the centuries, the same fundamental structure is to be discerned. It comprises two equally essential elements: on the one hand, the acts of the man who undergoes conversion through the action of the Holy Spirit: namely, contrition, confession, and satisfaction; on the other, God's action through the intervention of the Church. the Church, who through the bishop and his priests forgives sins in the name of Jesus Christ and determines the manner of satisfaction, also prays for the sinner and does penance with him. Thus the sinner is healed and re-established in ecclesial communion.