Day 198: Reconciliation With God

Sin is before all else an offense against God, a rupture of communion with him. At the same time it damages communion with the Church. For this reason conversion entails both God's forgiveness and reconciliation with the Church, which are expressed and accomplished liturgically by the sacrament of Penance and Reconciliation. CCC 1440

The Catechism discusses the Sacrament of Reconciliation and Penance in today's short reading, particularly reconciliation with God and the Church. Scripture is clear that we sin (Ecc 7:20), even if we deceive ourselves to believe otherwise (1 Jn 1:8), and such is an offense to God (Isa 59:2). Only God can forgive sins (Lk 5:21) and Christ through His Apostles has shared this power to the Church to exercise it in His name (Jn 20:21-23). Through this "ministry of reconciliation," the Church acts "on behalf of Christ" to bring us all to God (2 Cor 5:18-20). This authority includes reconciling repentant sinners with the Church (Mt 18:18) for "Reconciliation with the Church is inseparable from reconciliation with God" (CCC 1445).

The Catechism Companion, Vol II has some good commentary on this:

Sin is an act of choosing one's own will over God's will, rejecting his authority and love. Sin also causes disunity within the Church, the family of God, and the Body of Christ... Being reconciled to God and being reconciled to the Church are both needed, requiring forgiveness and restoration... Forgiveness involves releasing the debt owed by the sinner, while reconciliation restores the relationship. We may forgive others without being reconciled, but God restores us with both forgiveness and reconciliation in the sacrament. (p. 160)