I've heard that at the Final Judgment, each soul has to make account of his sins.
According to Scripture:
2 Corinthians 5:10 For we must all appear before the judgment seat of Christ, so that each one may receive recompense, according to what he did in the body, whether good or evil.
The Catechism says:
1039 In the presence of Christ, who is Truth itself, the truth of each man's relationship with God will be laid bare.626 The Last Judgment will reveal even to its furthest consequences the good each person has done or failed to do during his earthly life:
All that the wicked do is recorded, and they do not know. When "our God comes, he does not keep silence.". . . he will turn towards those at his left hand: . . . "I placed my poor little ones on earth for you. I as their head was seated in heaven at the right hand of my Father - but on earth my members were suffering, my members on earth were in need. If you gave anything to my members, what you gave would reach their Head. Would that you had known that my little ones were in need when I placed them on earth for you and appointed them your stewards to bring your good works into my treasury. But you have placed nothing in their hands; therefore you have found nothing in my presence."
What about the sins we confessed in the Sacrament of Confession? Aren't they forgiven and forgotten?
Yes. They are forgiven and forgotten before you get to the Judgment Seat. But not before Final Purification. Let me back up.
They are forgiven. But there remains a price to pay for the "temporal consequence" of the sin.
Baptism washes away sin. There is nothing that remains of sin when one is baptized. No temporal consequence. Even Original Sin is washed away. Nothing remains. If a person dies right after Baptism, without having committed any other sins. He will have a clean slate when he appears before the Judgment Seat.
Confession is different. If a man is baptized and then commits sin again, as most of us do. He must return to the fountain of grace, the Sacrament of Confession and ask forgiveness. The sin is forgiven, if the man is sincere. But, there remains a "temporal consequence" which must be atoned by suffering or by doing good deeds.
For me, the best illustration of this concept is in the Bible, when King David had an adulterous affair with Bathsheba and murdered her husband. God sent the Prophet Nathan to visit him and the story goes like this:
2 Samuel 12:
Nathan's Parable. 1 The Lord sent Nathan to David, and when he came to him, he said: “Tell me how you judge this case: In a certain town there were two men, one rich, the other poor. 2 The rich man had flocks and herds in great numbers. 3 But the poor man had nothing at all except one little ewe lamb that he had bought. He nourished her, and she grew up with him and his children. Of what little he had she ate; from his own cup she drank; in his bosom she slept; she was like a daughter to him. 4 Now, a visitor came to the rich man, but he spared his own flocks and herds to prepare a meal for the traveler who had come to him: he took the poor man’s ewe lamb and prepared it for the one who had come to him.” 5 David grew very angry with that man and said to Nathan: “As the Lord lives, the man who has done this deserves death! 6 He shall make fourfold restitution for the lamb because he has done this and was unsparing.” 7 Then Nathan said to David: “You are the man!
Nathan’s Indictment. “Thus says the Lord God of Israel: I anointed you king over Israel. I delivered you from the hand of Saul. 8 I gave you your lord’s house and your lord’s wives for your own. I gave you the house of Israel and of Judah. And if this were not enough, I could count up for you still more. 9 Why have you despised the Lord and done what is evil in his sight? You have cut down Uriah the Hittite with the sword; his wife you took as your own, and him you killed with the sword of the Ammonites. 10 Now, therefore, the sword shall never depart from your house, because you have despised me and have taken the wife of Uriah the Hittite to be your wife. 11 Thus says the Lord: I will bring evil upon you out of your own house. I will take your wives before your very eyes, and will give them to your neighbor: he shall lie with your wives in broad daylight. 12 You have acted in secret, but I will do this in the presence of all Israel, in the presence of the sun itself.”
David’s Repentance. 13 Then David said to Nathan, “I have sinned against the Lord.” Nathan answered David: “For his part, the Lord has removed your sin. You shall not die, 14 but since you have utterly spurned the Lord by this deed, the child born to you will surely die.” 15 Then Nathan returned to his house.
Notice that God forgave King David. But read the underlined words. All those punishments came to pass. If you read on, you will see that David's own son tried to kill him, chased him out of the Kingdom and slept with David's wives on the roof of his house so that all of Israel could witness it. Not only that, but his children went to war with one another and his Kingdom was divided.
God forgave David, yet David had to pay for the "temporal" consequences of his sins.
We also must pay. God was kind enough to send His only begotten Son to die for our sins upon the Cross. Thus, we were washed of those sins in Baptism. He made us Priests, Prophets and Kings. And God then made us part of His household. God made us His own children. But then we chose to sin again. For His part, God forgives us, if we repent. But, we must pay for the temporal consequence of these sins, ourselves.
If we haven't paid for them before we die, we will be cleansed of them in Purgatory. The Final Purification.
Now, when we appear before the Judgment Seat. Our sins, which we confessed in the Sacraments, are forgiven and forgotten.