The flesh is incurably bad. "It is not subject to the law of God, neither, indeed, can be." It never can be any better. It is no use trying to improve the flesh. You may educate it all you please. You may train it by the most approved methods, you may set before it the brightest examples, you may pipe to it or mourn to it, treat it with encouragement or severity; its nature will always be incorrigibly the same.
Like the wild hawk which the little child captures in its infancy and tries to train in the habits of the dove, before you are aware it will fasten its cruel beak upon the gentle fingers that would caress it, and show the old wild spirit of fear and ferocity. It is a hawk by nature, and it can never be made a dove. "For the carnal mind is enmity against God. It is not subject to the law of God, neither, indeed, can be."
The only remedy for human nature is to destroy it, and receive instead the divine nature. God does not improve man. He crucifies the natural life with Christ, and creates the new man in Christ Jesus.