Hi Bookends,
No doubt you think of 'sin' as bad behavior and in those terms I agree with you that we are not perfect. So I can assure you I am not one of those self-righteous legalists who preach perfect obedience to the law (or some allegedly higher ambiguous code of behavior) is to be achieved as proof of your salvation.
But, how we define "sin" is important. It helps us understand scripture correctly.
Unfortunately man's traditional definitions of "sin" are ambiguous. Whilst we do not live perfect lives in this physical (and God disciplines us should we do wrong), this imperfection is not defined as sin in scripture.
Instead, God has given us specific definitions which are the only ones to use to understand scripture.
God’s definitions of sin are basically covered by the following examples:
1: Mark 3:29 Blasphemy of the Holy Spirit. This sin will not be forgiven. Christians do not commit this sin.
2: John 16:9 Unbelief in Jesus. This is the sin the world is convicted of. Christians do not commit this sin either.
3: 1John5:17 “all unrighteousness is sin”. Christians are righteous in Christ so here we do not sin.
4: 1John3:4 “Sin is transgression of the law”. This is breaking the 10 commandments resulting in a death penalty for transgression.
Christians cannot be accused of sin here as we are not under the law of sin and death.
The law of the Spirit of life in Christ Jesus sets free from the law of sin and death, (Rom 8:2).
Regarding the law of sin and death it should be noted that:
“whatever the law says it says to those who are under it” (Rom 3:19).
“the law was not made for a righteous person (Christians), but for…the ungodly and for sinners” (1Tim 1:9).
“where there is no law there is no transgression (SIN)” (Rom 4:15).
We know sin was dealt with once and for all on the cross.
And “Our old man is crucified with Christ, that the body of sin might be destroyed” Rom 6:6.
Hence we see in 1Pet 4:1 “Therefore, since Christ suffered (crucified) for us in the flesh, arm yourselves also with the same mind (our old man crucified with him. Rom 6:6), for he who has suffered in the flesh (Rom 6:6) has ceased from sin”.
And note Rom 3:25: "Whom God hath set forth to be a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past,"
It was only our past sins that were forgiven. That means there is no more forgiveness of sin after this as sin was finally dealt with.
And this is confirmed by the following scriptures:
1Pet 4:1 that we have 'ceased from sin'.
1John3:9 “Whoever has been born of God does not sin, for His seed (Christ) remains in him; and he cannot sin, because he has been born of God”.
Rom 6:2 asks “How shall we that are dead to sin, live in it any longer?”.
Finally, consider 1Pet 4:18 “If the righteous scarcely be saved, where shall the ungodly and sinner appear”.
Clearly there are 2 different groups described here.
Group 1: Righteous (and saved).
Group 2: Ungodly/Sinner (unsaved).
Either we are righteous (in Christ) OR we are sinners. We can't be both.
Truly Jesus set us free from sin (John 8:36).
Now, as a believer, we are no longer a sinner deserving of death. We are children of God, righteous, holy (Rom 11:16), sanctified (Heb 10:10), perfected (Heb 10:14) and cannot sin (1John 3:9), by Christ's one offering. It is Christ in us that imputes this to us, just as with the thief on the cross.