If you looked at the context of CCC 1475 instead of ripping it out you would see that it is not referring to atoning for the eternal consequences for sin - the punishment due to our offence against God. That is what Jesus did for us.
But when we sin we also damage ourselves - we turn towards things in creation that we put before God. We also damage others. If I steal a £1,000 from someone they are £1,000 poorer. I need to repent and ask God's forgiveness for that sin but should also make amends for what I have done to the other person - ideally by paying back the £1,000. We have to make some form of satisfaction.
Many sins wrong our neighbor. One must do what is possible in order to repair the harm (e.g., return stolen goods, restore the reputation of someone slandered, pay compensation for injuries). Simple justice requires as much. But sin also injures and weakens the sinner himself, as well as his relationships with God and neighbor. Absolution takes away sin, but it does not remedy all the disorders sin has caused.62 Raised up from sin, the sinner must still recover his full spiritual health by doing something more to make amends for the sin: he must "make satisfaction for" or "expiate" his sins. This satisfaction is also called "penance." (CCC 1459). It is that form of expiation that 1475 refers to not the offence against God.
Of course it's God that purifies us and makes us holy.
But on what basis? What is our part in the purification process?
Here is the scriptural support
1. God is holy and perfect, and He tells us to be holy and perfect as he is holy and perfect.
“…but as he who called you is holy, be holy yourselves in all your conduct; since it is written, "You shall be holy, for I am holy." (1Pet 1:15-16)
“You, therefore, must be perfect, as your heavenly Father is perfect.” (Mt 5:48)
2. Unless we are clean (holy and perfect) we will not enter heaven for a life of communion with God.
“But nothing unclean will enter it” [The new Jerusalem – Heaven] (Rev 21:27)
3. Unless we are holy we will not see God.
“Strive for peace with all men, and for the holiness without which no one will see the Lord” (Heb 12;14)
Note that we are exhorted to strive for it.
4. When we are initially justified (I believe by baptism) God makes us holy and perfect.
“When the goodness and loving kindness of God our Saviour appeared, he saved us, not because of deeds done by us in righteousness, but in virtue of his own mercy, by the washing of regeneration and renewal in the Holy Spirit, which he poured out upon us richly through Jesus Christ our Saviour, so that we might be justified by his grace and become heirs in hope of eternal life.” (Ti 3:4-7)
5. But during our life we sin which disfigures and soils our souls and from which we need cleansing to restore us the holiness and perfection necessary to enter heaven. This is an ongoing process of sin, repentance, and cleansing.
“Since we have these promises, beloved, let us cleanse ourselves from every defilement of body and spirit, and make holiness perfect in the fear of God.” (2Cor 7:1)
Again we are told we have to do something.
If we are not wholly clean, holy and perfect there must be some process whereby we can be cleansed and made holy and perfect. Scripture tells us there is.
In Hebrews 11 the writer describes the faith of many of those in the Old Testament, men and women, from Abel onwards. At the end he writes:
"And all these, though well attested by their faith, did not receive what was promised, since God had foreseen something better for us, that apart from us they should not be made perfect."
These people were all dead, but they had not been made perfect. They had not received what was promised (heaven).
Then he writes:
"Therefore, since we are surrounded by so great a cloud of witnesses, let us also lay aside every weight, and sin which clings so closely, and let us run with perseverance the race that is set before us" (12:1). These faithful people of the Old Testament are now witnessing our struggles. This can only be from heaven. But you have to be perfect to be in heaven. So those that were not perfect must have been made perfect
And he confirms this later in the chapter.
“But you have come to Mount Zion and to the city of the living God, the heavenly Jerusalem, and to innumerable angels in festal gathering, and to the assembly of the first-born who are enrolled in heaven, and to a judge who is God of all, and to the spirits of just men made perfect” (Heb 12:22-23)
These just men were not perfect when they died but they are now. This shows that there is a way, a process, whereby the spirits of just men can be made perfect after death.
God in his mercy has provided a final purification process whereby we are made fit to enter his presence.
Catholics call this process Purgatory.
“The Church gives the name Purgatory to this final purification of the elect, which is entirely different from the punishment of the damned.” (CCC 1031)
Protestant scholars say differently
