@Life,
A person is either "UNDER" the law or they are "UNDER" Grace; you cannot be "UNDER" both. Believers are not "UNDER" the law (at all), but "UNDER" Grace (Rom. 6:14).
If a person is "UNDER" the law and breaks the law, that person has sinned. If a person is "NOT UNDER" the law, that person "cannot sin" or have the "knowledge of sin" because the law does not say to them they've sinned.
Now we know that "whatever" the law" says, it saith to them who are "UNDER" the law: that every mouth may be stopped, and all the world may become guilty before God. Therefore by the deeds of the law there shall no flesh be justified in his sight: for "by the law " is the "knowledge of sin" (Rom. 3:19, 20).
If a person says they sin, it's because they are under/justifying themselves by the law - ignorantly or not. The law has "dominion and power" over a person under it and "imputes sin" unto that person if they stumble "one" time.
1 Cor 15:56; The sting of death is sin, and the power of sin is the law;
The power of "sin" is the law because a person "under that law" is subjected to what the law says. A believer "UNDER" Grace is not subjected to the law imputing sin unto them, because they are not "UNDER" the law. The law "ONLY" imputes sin to those that are "sinners" and those that "justify" themselves by the law. A person cannot know they've sinned unless they are "UNDER" the law. It is only by the law that a person has the knowledge of sin.
Romans 3:19
Now we know that whatever the law says, it says to them who are under the law: that every mouth may be stopped, and all the world may become guilty before God.
Romans 3:20
Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin.
"Jas 2:10; For whoever keeps the whole law and yet stumbles in one point, he has become guilty of all."
This scripture is saying a person is guilty before God which confirms Romans 3:19. A person is "ONLY" guilty if they are "UNDER" the law. If a person is "NOT UNDER" the law, God is not "imputing sins" unto that person. Therefore, they will not feel guilty because they have no knowledge of sin.
Romans 5:13
For until the law sin was in the world: but sin is "not imputed" when there is no law.
Romans 4:7, 8
Saying, Blessed are they whose iniquities are forgiven, and whose sins are covered. Blessed is the man to whom the Lord will not impute sin.
God is not imputing sins unto believers in two ways. First, the believer is not under the law, therefore, sin cannot be impute. Secondly, Jesus came and took man's sins upon Himself by God imputing all man's sins unto Jesus Christ, and then imputed the righteousness of Christ unto believers. Because Christ condemned sin, He was "quickened" from sin - and every person that believes in Him is also "quickened" from sins and reaps the benefit of Christ in the Spirit. Believers are in the spiritual body of Christ, and Christ is in the body of believers. The body of believers have become the temple of the Holy Ghost once their sins have been circumcised, (out of their body), and they have been given a new heart (1Cor. 6:19, 20; Eze. 36:26).
Colossians 2:11
In whom also you are circumcised with the circumcision made without hands, in putting off the body of the sins of the flesh by the circumcision of Christ:
Jesus Christ has cut out the sin nature that was in the body of believers that He may come and reside in the hearts of believers. Sin has been crucified and condemned (through faith) in the body of all believers.
Colossians 2:13
And you, being dead in your sins and the uncircumcision of your flesh, hath he quickened together with him, having forgiven you all trespasses;