I'm not sure it is possible to hold both positions simultaneously. Either Christ is the perfection in us, or we are ourselves perfect souls living in mortal bodies. When we are "Born Again" we do receive a New Nature. But as much as it is created to be like Christ it is not perfect as Christ is.
For me, a "New Nature" simply means that our souls have received fresh spiritual life from Christ--not that it is an entirely new, immortal entity living inside a mortal body.
You said:
"Are you saying we have sin excised from our flesh,"
Yes, by Jesus. He cleansed us from ALL unrighteousness. That wouldn't be true if he didn't take away the source of sin, the DESIRE to sin in our our nature. A clean nature lets us partake of the divine nature of God.
or are you just saying that we have a pure nature from Christ existing within our sin-infected mortal bodies?
Our mortal body will die because of sin - Adam's sin. But we have a clean nature from Christ AND He lives inside.
By "taking away our sins" John is meaning that *legally* our sins are erased--not that we have in any way become perfect yet.
Not perfect, because that means the maturing also of all the fruit of the Spirit. But we are sinless on day one of having all our sins
taken away (not just
covered like a screen over a cesspool which is a false teaching). Run from any teacher that uses the word "covered," because that is Old Testament and ignorant.
In context Paul was talking about the complementary aspects of the Law and the Gospel of Grace. Both established righteousness as the rule for Man, since we were all created in the image of God. Both the Law and the Gospel established that reality.
The change from the Law of Moses to the Covenant of Grace was an intended and natural progression, rather than a rebuttal against living by the rules of the Law. Once Christ died for sin, animal sacrifices were no longer needed. But living by the moral guidance of the Spirit of God did not change at all. Again, this has nothing to do with our adopting perfect natures through Christ!
Adopting perfect natures through Christ? It isn't us, but the Author and Finisher of our faith. The difference between the laws of God from the Old to the New Covenants is the Spirit. Under the Old Covenant, the Jews had to keep laws in opposition to their sin nature. In the New Covenant, because of the cleansing of the desire to commit lawlessness out of our nature, and the indwelling Spirit, we keep God's laws naturally.
We agree on our need to be righteous, that we are not "Sinners" in the sense we remain "Sinful" and do not reflect the introduction of Christ's renewing life into our lives.
We are not sinners, period. We are children of God. We "keep ourselves" meaning we obey our conscience. 1 John 5:18 "We know that whoever is born of God does not sin; but he who has been born of God keeps himself, and the wicked one does not touch him.
1 John 3:3 "And everyone who has this hope in Him purifies himself, just as He is pure."
Both of those would be impossible to do with a sin nature present. Once clean, it is easy to keep ourselves that way. The Spirit in us sensitizes us to not sin in the first place. Seeing as abiding in Christ is the reason we can "keep ourselves" we already have the requirement for maturing all the fruit of the Spirit.
I am not teaching Sinless Perfection as that doesn't exist. I teach righteousness which is sinlessness, and is DAY ONE. Then towards the end of our life if we have been abiding in Christ we mature in the fruit and become like Christ - perfect. That is holiness. And both sinlessness and perfection can be in this lifetime. Otherwise when we die, we couldn't be holy as Revelation 22:11 says. It has nothing to do with our body as is taught by false teachers.
This has to do with legal resolutions, and not with our supposed metamorphosis from being a Sinner to being Sinless.
Just as it is not a myth that Jesus died a horrible death, sinlessness is absolutly real. When I was born again in 1977, I literally felt a heaviness lift out of me and I was completely freed of lawlessness. I had been struggling with adultery. The next day I was free. There is no struggle to be righteous after being filled with the Spirit, and this was after 30 years of going to church!
I would phrase it differently. To be holy is to conform our lives to the holiness of God. We simply adopt Christ as our life and forsake the selfishness of human carnality. We avoid wants, lusts, and anything independent of God. Fruit does not make us holy, as such, but is only the result of our choice to conform to God's holiness. If we choose to live in conformity with His will, we will produce His fruit of love and kindness.
You are not the author and finisher of your faith. It is the POWER OF GOD only. Our only involvement is not quenching the Spirit.