If you believe Christians don't sin , what will you tell Apostle Paul who spoke of the agony & conflict with having two natures?
Romans 7:14-25
"14For we know that the Law is spiritual, but I am of flesh, sold into bondage to sin. 15For what I am doing, I do not understand; for I am not practicing what I would like to do, but I am doing the very thing I hate. 16But if I do the very thing I do not want to do, I agree with the Law, confessing that the Law is good. 17So now, no longer am I the one doing it, but sin which dwells in me. 18For I know that nothing good dwells in me, that is, in my flesh; for the willing is present in me, but the doing of the good is not. 19For the good that I want, I do not do, but I practice the very evil that I do not want. 20But if I am doing the very thing I do not want, I am no longer the one doing it, but sin which dwells in me.
21I find then the principle that evil is present in me, the one who wants to do good. 22For I joyfully concur with the law of God in the inner man, 23but I see a different law in the members of my body, waging war against the law of my mind and making me a prisoner of the law of sin which is in my members. 24Wretched man that I am! Who will set me free from the body of this death? 25Thanks be to God through Jesus Christ our Lord! So then, on the one hand I myself with my mind am serving the law of God, but on the other, with my flesh the law of sin."
Like many people who don't look for context, you started with verse 14, but verse 13 tells the context 14-23 should be seen in. Then chapter 8 makes more sense. The reason why the unsaved, who actually know the law like the OT Jews and Pharisees, can't keep the law is sin in the original carnal nature inherited due to Adam's first sin. That is what Jesus' death dealt with, the carnal nature, and why He is called the second Adam, and is exactly why we need to be born again of the Spirit. That is what makes us dead to sin. The Spirit. What you quoted is those under the law only without the Spirit. But Paul is comparing that state with chapter 8 of introducing the Spirit through Christ Jesus. It is LAW vs. SPIRIT. Those that repent of their sin are cleansed of all their past sin, but Jesus doesn't stop there. He then gives us His Spirit to make us not desire to sin in the present and future. False doctrine teaches the opposite - that we will always have to battle the flesh. But Jesus condemns sin in the flesh, and if we are in the Spirit, then we will not fulfill the lust of the flesh. It is up to us to not grieve or quench the Spirit, because then we are like a dog going back to eat up his own vomit. We cannot live in two realms - the Spirit and the flesh. The saved stay walking in the Spirit. Those who do not stay in the Spirit, start to love sin more, and again become slaves of sin.
Romans 7:13
13 Has then what is good become death to me? Certainly not!
But sin, that it might appear sin, was producing death in me through what is good, so that sin through the commandment might become exceedingly sinful.
Romans 8:2
2 For the law of the Spirit of life in Christ Jesus has made me
free from the law of sin and death. 3 For what the law could not do in that it was weak through the flesh, God
did by sending His own Son in the likeness of sinful flesh, on account of sin:
He condemned sin in the flesh, 4 that the righteous requirement of the law might be fulfilled in us who
do not walk according to the flesh but according to the Spirit.