Venial sins can be, but mortal sins can only be forgiven through the sacrament of penance. Although it is recommended to confess venial sins in the sacrament of penance as well.
Reconciliation is very important because through the sacrament of reconciliation you are sure that your sins are forgiven. Unlike Christians who pray silently and are not sure if their sins are forgiven, we can be sure. We confess with the priest and say our penance; we know that if we die at that moment we would go to heaven and have no sins in our souls. There are two types of sins mortal and venial; someone who dies with a mortal sin in their soul has little chance of making heaven.
Catholics must confess their sins to a priest as this is the only normal way in which Our Blessed Savior left for people to have their sins forgiven. Less serious sins (venial sins) may be forgiven with a good Act of Contrition and Holy Communion. Serious sins (mortal sins) may only be forgiven at Confession. Besides the Church requires that all adult Catholics must go to confession at least once a year, even if they have not committed any mortal sins. Any good Catholic who is sincerely trying to fall Christ and become perfect (Matthew 5:48) should be going to regular confession, weekly or at the least, every other week.
Of course, the only sins which cannot be forgiven are the unforgivable sin which is the sin against Hope (the second of the Cardinal Virtues). The sins against hope which cannot be forgiven are presumption and despair.The former is akin to the Protestant theory that once you are "saved" you cannot do anything to lose your salvation. That is presumption and is unforgivable as you don't think you need forgiveness.The latter, despair, is unforgivable as you don't think you can be forgiven for whatever reason: you think you have committed too many sins, or too horrible a sin, or whatever.The sins against hope cannot be forgiven for the simple reason that you cannot be contrite and ASK for forgiveness. God will forgive ANYTHING as long as we repent of it - which is not just being sorry for it, but trying not to do it again.Sins which we have not yet done cannot be forgiven until AFTER we do them, and repent of them. But all mortal sins can be forgiven as long as we confess them and repent. It is only when we are not contrite and repentant that we cannot be forgiven.
Sins that are confessed to a priest and proper penance was observed, such sins are forgiven and not accountable and need not be confessed again.
There is no precise list of mortal sins in the Catholic Church.
All sins can be forgiven in may ways because God can do all things
If you are absolved in the sacrament of penance.
so that their sins are forgiven
Mortal sins are more serious than venial sins, and they have more serious consequences: With mortal sin, the life of grace is lost and the sinner is in danger of hell. With venial sin, the life of grace is weakened but not lost. Even so, venial sins should not be taken lightly, since habitual venial sins can harden one to commit mortal sin.
Roman Catholic AnswerIs it necessary? Strictly speaking, no, practically speaking, yes - for mortal sins. All mortal (serious sins that kill the life of grace in the soul) sins must be confessed to a priest, at least once a year. It is never *necessary* to confess venial (less serious) sins although it is a good idea.I say strictly speaking, no, as if there is literally no way you can get to a priest, you may always confess your sins directly to God, and, in the impossibility of getting to confession, you can be reasonably sure they are forgiven IF YOU HAVE PERFECT CONTRITION. Now, keep in mind that perfect contrition is nearly impossible, and it is nearly impossible to be unable to get to a priest, so we are talking really abstract here.In the normal course of the way reality is, and the way Jesus set up His church, yes, one must go to confession at least once a year, and preferably more often for all mortal sins.
A venial is a slight offense against God while a mortal sin is a great offense. A venial sin is like a spiritual misdemeanor while a mortal sin is like a spiritual felony. Things like telling lies to get out of trouble, stealing something that is not of great value, or profanity are examples of venial sins. Murder (including abortion), stealing something of great value, and not going to Church on Sunday (which violates the Third Commandment) are examples of mortal sins. Mortal sins are so serious that they drive sanctifying grace from the soul. If you die without having been forgiven for a mortal sin, you will go to hell. Venial sins only lessen grace. No amount of venial sin is enough to send someone to hell. If you die without having been forgiven for venial sins, you will have to spend time in purgatory to have them forgiven. Really though, God looks at all sin the same. Read Rev. 21:8. Also, one scripture says why should we keep on sinning, is it so that grace may increase. If you don't repent from any kind of sin you will go to hell. If God sees the effort, you are fine because he understands nobody is perfect and we all mess up.