5. This corruption of nature remains in those who are regenerated during this life. Although it is pardoned and mortified through Christ, yet this nature itself and all the actions coming from it are truly and properly sin.
6. Every sin, both original and actual, being a transgression of the righteous law of God and contrary to it, by its nature brings guilt on the sinner, by which the sinner is bound over to the wrath of God and the curse of the law, and so made subject to death, with all manner of spiritual, temporal, and eternal miseries.
(WCF 6.5-6)
In the book of Romans, the Apostle Paul pulls back the curtin to allow us into a terrible struggle that he was having in his inner self, between his ‘flesh man’ and ‘spirit man’, saying “For I know that nothing good dwells in me, that is, in my flesh. For I have the desire to do what is right, but not the ability to carry it out. For I do not do the good I want, but the evil I do not want is what I keep on doing. Now if I do what I do not want, it is no longer I who do it, but sin that dwells within me" (Rom 7:18-20, ESV). Simply put, Paul was observing and speaking about what the confession is talking about here; though we are saved by grace through faith, This corruption of nature (being sin) remains in those who are regenerated during this life.
As we have observed through the weeks in our confession, our first father Adam was the root of all humanity, which the human tree has grown from and because the root was corrupted by sin, the whole human family has been tainted as well (WCF 6.3). So though it (being our sin) is pardoned and mortified through Christ, the stark reality of every Christian on the face of the planet is this - Though the war for your soul and eternity has been won by Jesus Christ, you’re now engaged in a battle that will last for the rest of your life, a battle between your ‘flesh’ and ‘spirit’, a battle to reject what was once so very natural to you (to reject the sin you once loved) to engage in picking up your cross and following Jesus on the straight and narrow (Matt 7:13-14, 16:24-26).
This is the wonderful news though, none of us are in this battle alone, no God is personally engaged and invested in His people because He has purchased us with the precious blood of His Son and filled us with His most Holy Spirit, and what He has begun in us, He will see it to completion (Rom 3:21-25, Eph 1:13-14, Phil 1:6). Thats why the born-again child of God struggles, strives and seeks to mortify sin because this nature itself and all the actions coming from it are truly and properly sin, thus it is offensive to our enlightened and tender conscience (Eph 1:18, 1 Tim 1:19). Every Christian struggles with our own wants and desires, but we will seek to kill the sin that so easily entangles us in the power of the Spirit because Jesus has become our master and we want to please Him and not grieve His Spirit in us (Rom 8:13, Heb 12:1-3 c.f. Eph 4:30). And so if you’re struggling and battling sin, take heart dear one, God is at work and He will never leave nor forsake you in the fight - but keep fighting because Every sin, both original (that which we inherited) and actual (that which we commit) is a transgression of the righteous law of God and thus brings guilt on the sinner by which the sinner is bound over to the wrath of God and the curse of the law from which we were once snatched from (Jd 1:23).
No true child of God desires to be a pig wallowing in the mire, but the bible does make clear that we are in danger of being like dogs returning back to it’s vomit, and that which you were delivered from becoming that much more worse (2 Pet 2:22, Matt 12:43-45), so resist sin in the power and knowledge of the gospel, because when we quench the Spirit and reject God’s word we make ourselves subject to death, with all manner of spiritual, temporal, and eternal miseries.