Q. Do you need a priest for confession? Why can't you say sorry by yourself and be good to receive?
A. Yes you need a priest.
1. Confession is a Sacrament and you can't give yourself a Sacrament e.g. you can't baptise yourself or make yourself a priest or give yourself confirmation. Similarly, you can't give yourself the Sacrament of Confession. Basically, you can't give yourself grace - much more so if you are spiritually dead through mortal sin.
2. All Sacraments work/are effective because Christ does something spiritual in us through them.
All Sacraments - like all humans - have two parts to them: a spiritual, immaterial part and a physical, material part. When dealing with mankind, when saving us, God deals and saves the WHOLE person soul AND body, spirit AND flesh, spiritual AND physical. God doesn't deal with us the same way he deals with angels; they have no body so God deals with them in an entirely spiritual way. Not so with us. Even when He wants to show us how much He loves us, He doesn't simply communicate that fact or truth with us mentally or spiritually. No. He does so in flesh, in something material, tangible. Jesus is the physical, tangible, material communication of God's love for us. Read John 3:16 again.
So all the seven Sacraments instituted by Christ for mankind also have both the spiritual and the material aspect: baptism has the material water and the immaterial words of Baptism; the Eucharist has the material bread and wine and the immaterial words of consecration. Confession has the material manifestations of sorrow/contrition of the penitent, and the immaterial words of absolution by the priest.
How can you be sure that you were indeed baptised, that your sins were washed away and that now you are an adopted child of God? Because that physical water physically touched your physical head! How can you be sure you have received the Body of Christ and fulfilled what he repeated severally in Jn 6? Because the physical bread that was consecrated by the priest, was physically placed on your physical tongue. The physical outward manifestations are a sign or proof of something spiritual and internal. The only way you know that some spiritual internal thing has happened is because a particular physical external thing happened. As with human love: we know that a spouse or mother loves us because of some physical, external manifestation. The same applies in the Sacrament of Confession: the words of absolution by the priest that I heard, are the assurance that something spiritual and internal has happened: the forgiveness of my sins.
3. That said, saying sorry to God - contrition - is an integral part of the Sacrament of Confession. God's mercy cannot wash a soul that is not sorrowful of its sins. God doesn't forgive us by force.
Christmas is coming!!!
22ndDecember 2015