Confession of Sin Before Priest is Biblical (Sacrament of Absolution is Very Important) And this Sacrament Sign was existed on Ancient Israel

 

An Israelite brought a Sheep as Burnt Sacrifice to Priest for Confession of His Sins

Israelites were queuing for confess their sins to Priest who offered the Burnt Sacrifice

Before Christ's coming to the world became a Human (still on His Pre-Incarnation as Word of God who became Angel of God, Burning Bush, and other before His coming became a Man), many Israelite were taught on Torah for confess their sins before Priest with bring a Burnt Sacrifice to Holy Priests. 

As for example, on Leviticus 5 teaches that Israelites must confess their sins before Priest :

" Let him do penance for his sin, And offer of the flocks an ewe lamb, or a she goat, and the priest shall pray for him and for his sin:  But if he be not able to offer a beast, let him offer two turtles, or two young pigeons to the Lord, one for sin, and the other for a holocaust,  And he shall give them to the priest: who shall offer the first for sin, and twist back the head of it to the little pinions, so that it stick to the neck, and be not altogether broken off.  And of its blood he shall sprinkle the side of the altar, and whatsoever is left, he shall let it drop at the bottom thereof, because it is for sin.  And the other he shall burn for a holocaust, as is wont to be done: and the priest shall pray for him, and for his sin, and it shall be forgiven him.

 And if his hand be not able to offer two turtles, or two young pigeons, he shall offer for his sin the tenth part of an ephi of flour. He shall not put oil upon it, nor put any frankincense thereon, because it is for sin:  And he shall deliver it to the priest: who shall take a handful thereof, and shall burn it upon the altar for a memorial of him that offered it:  Praying for him and making atonement: but the part that is left, he himself shall have for a gift. "  (Leviticus 5:5-13) 

And about the purification of woman after childbirth, woman must be cleansed with giving burnt sacrifices or other offering to the Priest for cleaning her sins :

" And when the days of her purification are expired, for a son, or for a daughter, she shall bring to the door of the tabernacle of the testimony, a lamb of a year old for a holocaust, and a young pigeon or a turtle for sin, and shall deliver them to the priest:  Who shall offer them before the Lord, and shall pray for her, and so she shall be cleansed from the issue of her blood. This is the law for her that beareth a man child or a maid child. And if her hand find not sufficiency, and she is not able to offer a lamb, she shall take two turtles, or two young pigeons, one for a holocaust, and another for sin: and the priest shall pray for her, and so she shall be cleansed. " (Leviticus 12:6-8) 

Israelite Priests have power from God to absolve the sins for Israelites Before Christ. And this custome to be continued on New Testament which Lord Jesus Christ gave his power like his authority to disciples for absolve the sins from faithfuls :

It was still the first day of the week. That evening, while the disciples were behind closed doors because they were afraid of the Jewish authorities, Jesus came and stood among them. He said, “Peace be with you.” After he said this, he showed them his hands and his side. When the disciples saw the Lord, they were filled with joy. Jesus said to them again, “Peace be with you. As the Father sent me, so I am sending you.” Then he breathed on them and said, “Receive the Holy Spirit. If you forgive anyone’s sins, they are forgiven; if you don’t forgive them, they aren’t forgiven.” (John 20:19-23) 

Lord Jesus gave power to his disciples for forgive the sins

Confession of sin behind the confessional booth before the Priest, as Tradition from Catholic Faith. 

So, Sacrament of Absolution or Sacrament of Repentance is Biblical and to be fulfilled with Catholic Priests who give absolution or forgiveness of the sins for faithful as sustainability from what Old Testament Teaching and what Jesus taught to his disciples. 

And then Isn't God All-Forgiving and All-Merciful? Why should peoples confess their sins to a priest? Confession is needed to declare oneself, besides confessing person's sins before a priest, that person has also expressed regret for all that person's sins, and indeed God is All-Merciful, so He has taken that into account from the beginning when the person wanted to confess. Everything has been recorded by God Himself based on the intention of the person confessing. The need for Confession does not mean that God's All-Merciful Characteristic is limited to the Burnt Offering brought to the priest or bringing one's confession to the confessional booth before the priest, but as a statement of oneself and also a form of regret for the person which must be witnessed by someone whom God has given His Power so that the person not only regrets himself, but also feels ashamed of the sins he has committed. That is the wisdom of why God bestowed the Sacrament of Confession. God can forgive the sins directly without Priest because He is The Most All-Forgiving and The Sacrament is not a limit on God's mercy, but a gift of mercy—a specialized "field hospital" for the soul that provides specific remedies and graces for specific sins, that's why Sacrament of Absolution or Sacrament of Confession is Most Important for True Christians or Faithfuls. 

Note: While Catholics must make an act of perfect contrition (sorrow based on love of God) to be forgiven, the Church still requires the intention to confess that sin to a priest as soon as possible. 

This also refutes the Protestant heresy that rejects the Sacrament of Confession, which originates from most Calvinists, Arminians, Zwinglians, Presbyterians, and many other Protestants reject this Sacrament and erase this Sacrament from their religion. (For more know about Protestantism Heresy, please read it : https://romancatholictraditional.blogspot.com/2025/04/catholic-church-with-council-of-trent.html ) 

Lutherans also teach Confession, but only as an option, not an obligation, and do not place much emphasis on it due to their Sola Fide heresy.