Rom 8;7 Because the carnal mind is enmity against God: for it is not subject to the law of God, neither indeed can be.
Walking in the Spirit versus walking in the flesh is more than a mindset or a habit.
It is two spheres, two worlds, grounds or soils.
The flesh in itself is not evil.
3 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 flesh, and for sin, condemned sin in the flesh:
Christ came in the flesh and died for sin in the flesh.
The problem with the flesh is that because of the law of sin and death lodged in its bodily members, it can be used as a beach head for the operations of sin.
Thus, the result of walking in the soil of the flesh will sooner or later yield its natural fruit, coming from its soil, which is death.
The law of sin and death which governs the grounds of the flesh will function to produce this fruit of death.
It is impossible in the sphere or the soil of the Spirit for the motions of sin to operate.
In the world or soil of the Spirit it is impossible for a trace of sin to be found.
As a matter of fact the soil or grounds of the Spirit are controlled by the law of the Spirit of life which naturally causes it to yield the fruit of righteousness, life and peace.
Therefore, waking in the Spirit versus walking in the flesh are two different worlds, and two different ways of living, and in them, are the different set of laws which govern these worlds causing different fruit to be naturally yielded.
The carnal mind is hostile to God simply because it functions in the world of the flesh.
It’s impossible for the carnal mind to subject itself to the laws which dominate the world of the Spirit or yield its fruit, when it lives in this different world and partakes from the fruit of its soil.
Therefore the carnal mind lives in constant hostility to God, and with that all humanity which functions out of a carnal mind is also hostile to God.