As a Christian, and a Roman Catholic at that, I was brought up with some pretty weird ideas about sin and forgiveness. About repentance, purgatory, heaven and hell, and ideas of venial and mortal sins. Venial sins, however, can be washed off. You can put venial sins right again, rub them out. Mortal sins, on the other hand, well, that s a different matter.
Mortal sins are like indelible ink.
You can wash them a bit and get rid of some of it. You can fade the stain made by mortal sins, but, sorry, you can t get rid of them. That is only possible in purgatory. So you will have to suffer some when you die before you can experience the true beauty and purity of God in heaven. But that s not it.