When a person accepts Jesus as Lord and savior the forgiveness of the sins is up to that point everything that you've done in your past the percent of Adam everything up to that point is Forgiven now it's up to us to continue to strive as Paul States just drive to be holy before God. Jesus tells us be holy as I am Holy. He's not saying that you're going to remain holy as I am Holy but it will you need to try to be holy as he is holy. The once they've always saved crowd feels that once you accept Jesus as your lord and savior you can do no wrong and that's a false statement right there. The fact is that you can do wrong and you can do some severe things wrong. It doesn't stop you from being a member of the flock and God's going to go way out of his way to help you but you can go to the point of rejecting God just like Judas did.
Understand that Judas Iscariot was one of those that was sent out in twos to go to the town and to preach and to remove demons from people and to heal people Jesus gave them the authority to do these things. And when they came back to Jesus they were ecstatic about all of the crazy things they had been doing. Jesus told them not to rejoice about all the things that they were doing but to Rejoice that their names were written in heaven.
This includes Judas Iscariot, his name was written in heaven Jesus said it himself. But he threw it away because he thought he had a better way to bring Jesus into the light of the Pharisees. He thought he could manipulate everything bringing Jesus to his crown as king of the Jews. And he betrayed Jesus in doing so.
Now remember Peter and Judas both rejected Jesus. But the difference between the two is what we need to pay attention too, where Peter repented from what he did, weeping bitterly. Where Judas hung himself. This is the difference between taking it upon yourself versus bringing it to God seeking his forgiveness of your sins.
So even though a person receives Jesus as Lord they still have to strive for the glory of Heaven and to be with the Father.
Now God knows us, he understands us and our failings. And even though we strive we still sin doesn't stop us from saying knowing God, knowing who Jesus is. We just have to keep reaching out to Jesus daily if we can seeking his forgiveness from our stupidity.
Purgatory is God's grace to us. Because you have to be perfect going into heaven, there is no sin in heaven. Think of it like being ritually pure. You have to be ritually pure to be in heaven.