You were cleansed from all sin when you believed the gospel and trusted in the cross of Christ, but you did not confess all your sins. You may have wrapped them all up together and said, ' Have mercy upon me a sinner' as the publican did in (Luke 18:13,14) and he went home justified.
In Luke 18:9-14, the Tax Collector cried out to God to have mercy on him. It's about acknowledging that you need a Savior and that you are sorry for your sin and you do not want to continue as a sinner. Matthew 12:41 says, the men of Nineveh will stand uup with this generation at the judgment, and will condemn it because they repented at the preaching of Jonah, and behold, a greater than Jonah is here. Jonah defines repentance as turning from their evil ways (See Jonah 3:9-10).
There are sins of ignorance (Lev 4) you did not confess including sins of your youth ( sins that involved the imaginations of your heart you did not confess, sins of the tongue you did not confess and if you say you have confessed all these things you have made yourself a liar and now you have the sin of lying to confess. And... how about theses sins in James 4:17 and in Rom 14:23? I can go on and show you about the years of sin before the law was given and how God related to those years in (Rom 5:5:12,13).
The Law of Moses is no longer binding. It was fulfilled with Christ's death upon the cross.
As for sins in the New Testament:
There are sins that lead unto death, and sins that do not lead unto death (See 1 John 5:16).
Paul lists those sins that lead unto death several times (Such as murder, lying, lusting, idolatry, theft, and drunkenness, etc.).
Therefore, as sin came into the world through one man, and death as the result of sin, so death spread to all men, [no one being able to stop it or to escape its power] because all men sinned.
13 [To be sure] sin was in the world before ever the Law was given, but sin is not charged to men’s account where there is no law [to transgress].
How was it that sin was not put on man's account before the law was given? Were these men responsible for their sin before the law was given? Now that Christ has come and put away sin, not imputing (or putting on man's account) their trespasses unto them in (2Cor 5:19) how is man judged according to his sins? I would suggest to you that this is where many of you have a problem because it has not been revealed to you by the Spirit through the written word, though is has been demonstrated to you through the death, burial and resurrection of Christ.
In Romans chapter 5 we learn, "For by one man sin entered the world and by one man many shall be justified."
Now, under the Mosaic Law there was an accounting and those under that Law had to bring their sacrifices accordingly. Prior to the Mosaic law, the Patriarchs offered sacrifices to God, but not as a result of particular sins–not because God said to them if you do such and such sin then you have to offer such and such sacrifices. The sacrifices of the Patriarchs were offered based upon faith, not law. Which explains the context of
Romans 5:13.
For sin was no doubt in the world prior to the law and so was transgression, hence there had to be some kind of law. For obviously Paul does not contradict himself here. He says that sin was not accounted until the law came. The point is that there was no law from God to this point that had been codified, that is, placed into written form. Before the Law of Moses, sin was not imputed because there was no written Law to transgress. Then how was sin imputed to those living before the written Law? Well, sin was imputed to those living before the Law because the "death of sin" was passed down to them thru Adam's disobedience (
Romans 5:12,
14,
17,
18,
19). Those living before the Law, were exclusively justified by faith and those who did not live by faith were condemned. In other words, the Old Testament saint living before the Law was justified by following
Romans 8:1. Yes, they did not know who Christ was yet or this passage, but the Spirit of Christ was in fact within the prophets, though (
1 Peter 1:10,
11).
This point of the Law in Romans 5 is made in Romans chapter 7. Compare
Romans 7:8-10 with
Romans 5:12-14 and
Romans 5:20.
Here is something else for you to wrap your mind around in (Psalm 25:6-8) ...
6 Remember, O Lord, Your tender mercy and loving-kindness; for they have been ever from of old.
7 Remember not the sins (the lapses and frailties) of my youth or my transgressions; according to Your mercy and steadfast love remember me, for Your goodness’ sake, O Lord.
8 Good and upright is the Lord; therefore will He instruct sinners in [His] way.
When you look at parallel passages of Psalm 25:8, you will see just how foolish your thinking is on this verse.
Psalm 25:8 - Parallel passages at Biblehub.