I've been studying Christianity once again and found out that there are two kinds of sins at the Roman Catholic Church -- 'venial' and 'mortal'. I found out that if one commits a mortal sin then it must be confessed in front of a priest in order to be completely forgiven. That scared me since I think I remember a couple of cases where I actually committed a mortal sin.
I've thought that since the categorization of sins doesn't seem to go the same way in the Bible, where all sins are seen as equally bad, I suppose, and since I'm a Lutheran myself, does this rule apply to me? Can I have all my sins forgiven just by asking for forgiveness from God in private prayer, or do I need to go to a priest for forgiveness every time I'm found guilty of what the Roman Catholic Church considers a mortal sin, in order to avoid going to Hell?
If you are interested in studying Christianity, it would seem that the best book to consult would be the one that defines it: the Bible.
As you noted, God never divided sins into categories like venial and mortal. All sins can lead to hell if the sin is not forgiven. As an example, "But the cowardly, unbelieving, abominable, murderers, sexually immoral, sorcerers, idolaters, and all liars shall have their part in the lake which burns with fire and brimstone, which is the second death" (Revelation 21:8) lists sins that are both considered by the Roman Catholic Church to be venial and mortal.
Nor do you find in the Bible any requirement for sins to be confessed to priests. For that matter, there is no separate priestly class in Christianity. All Christians are considered to be priests. "But you are a chosen generation, a royal priesthood, a holy nation, His own special people, that you may proclaim the praises of Him who called you out of darkness into His marvelous light" (I Peter 2:9). Confession of sin is made to God. "If we confess our sins, He is faithful and righteous to forgive us our sins and to cleanse us from all unrighteousness" (I John 1:9).
Only the one sinned against can offer forgiveness of the sin. All sin is against God, so only God can offer forgiveness. A man cannot offer forgiveness on behalf of God. See Must I confess my sins to a priest to be forgiven?
Just because some men make up rules to impose on others, it does not mean that God supports them. Man is supposed to conform to God's will, not the other way around. "He answered and said to them, "Why do you also transgress the commandment of God because of your tradition?" (Matthew 15:3). As Jesus asked, "But why do you call Me 'Lord, Lord,' and do not do the things which I say?" (Luke 6:46). See If Christ Built Only One, Where Did They All Come From?
Thanks for the response! I've been studying The Catechism of the Catholic Church and it's said there that Jesus gave the power to forgive all sins to the apostles that followed Him, and that the Catholic priests are their followers in the belief.
It is difficult to claim to be a follower of someone when you teach differently. The Roman Catholic Church has numerous doctrines that it admits are not found in the Bible. See The Roman Catholic church doesn't evolve, it realigns itself with the past.
I already noted that the concept of a priestly class within the church does not exist in the Bible. All Christians are priests (I Peter 2:9). Thus, if the claim is that priests can forgive sins, then all Christians would be able to forgive sins. Even under the Old Testament when there were priests, they did not have the right to forgive sins. You can see this when Jesus told the paralytic man that his sins were forgiven. The Jews became upset that a man claimed to do what only God could do (Matthew 9:1-2).
The verse you allude to that the Roman Catholic Church cites is John 20:23. See: