As a generalization, this is true.
There is however, a distinct difference between "willful" sin, and what would be better understood as "admitted" or confessed sin. The difference is in the heart. This is what Paul referred to saying that what he willed to do he did not do, but what he did not will to do, that he did...meaning his heart had changed--even completely, but the flesh was still weak.
I agree with this. Willful sinning is a heart of lust, that repents not. It is a heart that is set on personal sinning.
That is not the double mindedness you speak of in Romans 7, because there is still godly sorrow accompanying the repeated sinning by temptation. They still seek the grace of repentance to walk only after the Spirit, and no more after the flesh in Romans 8,
O wretched man that I am! who shall deliver me from the body of this death?
However, it's more accurate to say we would still have weakness
with our flesh, rather than our flesh having it's own weakness.
Sinfulness of man is with the flesh, not the flesh having sinfulness of it's own. While the KJV translation of being in the likeness of 'sinful flesh', is not inaccurate, I translate differently alongside 1 Tim 3:16: The Lord is come in the flesh,
after the likeness of sinful men, yet without sinning like all men.
For what the law could not do, in that it was weak through the flesh, God sending his own Son in the likeness of sinful men of flesh, and for sin, condemned sin in the flesh:
Or perhaps better stated: the flesh was still the flesh, and while he had been born again of the spirit (in heart), his flesh had not yet died.
In Romans 7, we have not yet
died to the flesh, as we ought. Our old man and life of sinning, is not fully crucified on our own cross.
When our mortal bodies do die, we will either be found doing righteously as He, or dying while sinning with the devil.
Which is were the grace of God comes in.
Not to cover continued sinning, but help with power not to continue sinning. Grace of God is the powerful help of Jesus not to sin in works of the flesh. It is not a powerful help to be covered, while sinning with the flesh.
Before Paul expressed the issue so, the grace of God was not much of a topic in the scriptures. Never before had sinful men walked without the law while remaining in sinful flesh. Of which he described, as "we who are alive and remain."
This is the sinful Gentiles without the law,
For as many as have sinned without law shall also perish without law: and as many as have sinned in the law shall be judged by the law;
It has nothing to with righteous saints in Christ Jesus, fulfilling the law righteously, by doing His righteousness under grace.
Jesus was the first, and we are to do the same and walk as He walked in our own lives.
To the contrary, those who actually "willfully" sin, actually don't have it in their heart not to do so.
Very true and well said: they cling to their lust and plan to do their sin, no matter what God or man says.
They are once again the old man returned to living on earth. There remains no more sacrifice for sinning, than before the old man was ever crucified on our cross in the first place.