I am not really sure how to effectively explain this. From my understanding it is like this:

1) God made Adam and Eve.

2) They made a mistake and ate the forbidden fruit. This was considered a sin, that would forever mean that everyone is born into sin, ie no one is perfect and without moral dillemma. 

3) To clense themselves of point 2, people had to sacrifice animals (the blood). That would give them a chance at going to Heaven. 

4) Christ was born, and his sacrifice was to negate the need to do point 3. Everyone is not able to go to Heaven.

5) While ppl can now go to heaven through Christ, that doesnt mean that the sins they committ are just automatically forgiven. 

washing away ppl's sins is washing away their inability to go to Heaven, It cleaneses the part of 'being born into sin', in that you cannot be perfect. Whereas any sin you comitt is still a sin and requires you t oask for forgiveness.

Since ppl dont sacrifice the animals anymore and therefore ask for forgiveness themselves at the same time, the process is now split into 2: Christ as the acrifice (no longer have to do) but asking for forgiveness still needs to be done. 

That is my understanding of how it works so the explanation is probably not entirely authentic. Hope this makes more sense .

Because to be forgiven one has to repent and also must show the true repentance to someone who can give the absolution. Which would be a priest, since shrinks, judges or lawyers aren't recognized by the Catholic Church (and thus by God). Also one isn't allowed to go to holy communion without having confessed first. 

Also it is interesting how Freud and Jung didn't invent much. The catholics have been doing that kind of "therapy" for centuries. Even for free! ^_^