After the legalization of the Church by Constantine, the Church fathers continued to emphasize the importance of confession. St. Ambrose (d. 397) wrote, "It seemed impossible that sins should be forgiven through penance; Christ granted this power to the Apostles and from the Apostles it has been transmitted to the office of priests" (De poenitentia). Similarly, St. Athanasius (d. 373) asserted, "As the man whom the priest baptizes is enlightened by the grace of the Holy Ghost, so does he who in penance confesses his sins, receive through the priest forgiveness in virtue of the grace of Christ" (Contra Novatus). By the mid-400s and the pontificate of Leo I, private confession under the seal of secrecy became the norm to safeguard the reputation of the penitent and to attract others to the sacrament.
Therefore, we go to confession because it is a sacrament given to us by Christ, and it has always been a practice of the Church. This sacrament reconciles us first with God: "The whole power of the sacrament of Penance consists in restoring us to God's grace and joining us with Him in an intimate friendship" (Catechism, #1468). Secondly, the sacrament reconciles us with the Church: "It must be recalled that… this reconciliation with God leads, as it were, to other reconciliations, which repair the other breaches caused by sin. The forgiven penitent is reconciled with himself in his inmost being, where he regains his innermost truth. He is reconciled with his brethren whom he has in some way offended and wounded. He is reconciled with the Church. He is reconciled with all creation" (John Paul II, Reconciliatio et paenitentia).
This sacrament is so important in our sharing in the life of Christ, the Church has even mandated its practice. To prevent laxity, the Fourth Lateran Council (1215) required that "every faithful of either sex who has reached the age of discretion should at least once a year faithfully confess all his sins to his own priest. He should strive as far as possible to fulfill the penance imposed on him, and with reverence receive at least during Easter time the sacrament of the Eucharist": This rule is still a precept of the Church, commonly called the "Easter Duty." The Council of Trent in 1551 in its Doctrine on the Sacrament of Penance asserted that since mortal sin "kills" the life of God in our souls, these sins must be confessed and absolved through the Sacrament of Penance (a principle repeated by Pope John Paul II in The Splendor of Truth). Trent also said "it is right and profitable" to confess venial sins.
We could end the answer here. However, regular confession is a healthy spiritual practice. Each sincere Catholic needs to periodically– every month or two– do a good examination of conscience holding himself to the standard of Christ. Each person should reflect on how well he has lived a "Christ like life" by following the commandments and the teachings of the Church. Perhaps one's failures are not so much commissions as they are omissions. For all of these, we bring our soul to the Lord and receive forgiveness. The healing grace of the Sacrament of Penance washes away sin and gives us the strength to avoid that sin again. The more we love the Lord, the more we are aware of the smallest sins and the more we want to say, "Lord, I am sorry. Please forgive me." I am sure this is why Pope John Paul II goes to confession weekly, as did Mother Teresa during her life. We too ought to take full advantage of this beautiful sacrament which draws us closer to the Lord.
https://catholicstraightanswers.com/why-go-to-confession/
Fr. Antonius David Tristianto, O.Carm.