As a practising Christian, the notion of repentance is an especially important one. Christ and the Church instructs us to repent for our sins. Many, including myself, a lot of the time mistake 'repentance' for a feeling of guilt or remorse for the sins that we have committed against God and also each other (which by extension is God again).
A sermon by Fr. Dimitri (i think it was him...) the other day reminded me that repentance is not merely an admission of guilt or remorse on our own part, which is really only the first (quite simple) step.
If we are to properly repent, we must really change the direction of our lives. Not only by feeling guilt and remorse for the many sins we have committed, but also to ask for forgiveness and totally change our lives to reflect our change in attitude to the sins we have committed, and to make our best effort not to continue doing so in the future. This is an important part of how us lowly humans can become closer to God.
Listening to that sermon the other day, it reminded me of the concept of a eucatastrophe. Everyone knows what a catastrophe is: a sudden, and possibly unexpected, change of events for the worse. Originally coined by JRR Tolkein (The author of Lord of the Rings), a eucatastrophe is the opposite of a catastrophe: a sudden, possibly unexpected, change of events for the better.
I couldn't help but think that that these two concepts are related: eucatastrophe and repentance. Although repentance is not necessarily a sudden change (it could take many months or years), it definitely should be quite a harsh change of attitude and 'events' to what existed previously.
Thus you could have the notion of eucatastrophic repentance of an individual: a sudden unexpected change in beliefs and attitudes of a sinful person that would constitute a complete '180' to travel in the direction of God, rather than continue down the opposite path.
As a note, i don't claim at all to be an expert on theology or Church beliefs or practices. I'm just ranting and raving on my thoughts.