Why does “sin” remain a relevant issue for the Christian subsequent to the imputation of Messiah’s righteousness?

First of all, sin, a violation of God’s moral law, results in enmity, seperation, between man and God as God is Holy and perfect in righteousness…God will not tolerate the destructiveness of sin in His presence or in His Kingdom (Revelation 21:27). Sin in the unsaved and disobedience in the saved in Jesus is a problem until the redeemed in Jesus rid themselves of this flesh, this body of death…please allow me to explain…

The struggle in the human condition is sin or violating God’s moral law because we are born from an earthly father, Adam, that introduced sin into human kind and through federal headship that sin is transferred genomically to every human being from Adam forward (Romans 5:12); theologically, this is referred to as a “sin-nature” (Romans 7:14-25) and the moment we attain an age of reason/accountability before God, the moment we are aware of our sin and our rebellion against the moral law infused within us and arbitrated by the conscience, we become culpable before God for our own sin (Deuteronomy 24:16; Jeremiah 31:30).

Combating the ramifications of sin is why Jesus Christ came into the World through the womb of the virgin woman; that is, to circumvent the sin-nature of Adam (Genesis 3:15; Matthew 1:23) as Jesus entered the Realm of Time to “destroy the works of the devil” (1 John 3:8b). Jesus walked this Earth in flesh for 33.5-years and fulfilled the moral law of God with absolute perfection (Matthew 5:17) thereby qualifying Himself as the ONLY acceptable atonement for our sin (Hebrews 10). God the Father, by Covenant, agrees to forgive the sin of and redeem anyone who will sincerely believe that Jesus is Lord who died to pay their sin-debt (John 3:16-18; Romans 10:9-10); furthermore, God the Father agrees to impute the perfection of Jesus into the life of the one who believes in Jesus as Lord (2 Corinthians 5:21) and subsequently Gift them the Holy Spirit to live in them and guide them in obedience to God’s will through the daily process of sanctification (Ephesians 1:13-14; John 14:16).

Though the redeemed = the faithful in Jesus Christ are “born again” by faith in Jesus as Lord and seek to walk in obedience to the Holy Spirit, the redeemed in Jesus, though they have a new nature that HATES sin (2 Corinthians 5:17; Galatians 5:16), the redeemed remain beleaguered with a sin-nature in the flesh that wars against the new nature in the Spirit (Ephesians 6; Romans 7; Galatians 5:16-26). It is this OLD sin-nature that, at times, causes us to behave in a way that interrupts intimacy with our Lord and the sin-nature will be a struggle until we exhale our last breath and rid ourselves of this body of death. Sin has been “the problem” beginning with Satan and his rebellion in the Kingdom; sin and free will are the foundation for God’s Law as Moral Law is the arbiter of free will.