Romans 6:6 Knowing this, that our old man is crucified with [him], that the body of sin might be destroyed, that henceforth we should not serve sin.

Knowing this, that our old man, the natural man, is subjugated, brought under control, conquered, and made subservient – with Christ, that the sinful nature might be subdued, that we should no longer obey or submit to it.
At regeneration, the power, which the natural man had, is loosed and the new man is established. It has been made subservient to the new man. This however, does not mean that the new man has become the ruling authority in the persons life. It also does not mean that the old man has been vanquished. However, if the person chooses to subdue the old man, he now has the ability to do so by exercising the new man. As we exercise the new man the new man subdues the old man. In Romans 8:7, Paul tells us that the carnal mind is enmity against God and is referring to the old mans way of thinking. In this passage, we are also informed that this old man is not subject to the law of God, neither indeed can be. It holds hostility that quickly results in active resistance and opposition to God. The old carnal man will not submit to God in obedience, and as affirmed here, cannot in any capacity. Those who are regenerated are able, through the Spirit, to subdue this carnal man. Choosing to walk after the Spirit, we subdue the carnal man, being filled with the Holy Spirit and renewing ourselves with the mind of Christ and submitting to the righteousness of God.
On the other hand, if we choose to allow the old man to rule our lives, it does not, nor is capable of, subduing the new man, since it has been conquered. In this instance, as we choose to allow the old man to enslave us once again, the new man retreats in accordance with our desires, but not without warning. This is the grieving of the Spirit, warning us that we are heading in the wrong direction, and if we do not heed these warnings, we can eventually quench the Spirit to the point that the warnings are no longer given.