The old man and the new man walked side-by-side. The old man is our flesh (old nature) and the new man is spiritual regeneration.
We all have two natures. As a result of these two natures we experience a conflict, the flesh against the spirit.
The flesh and the spirit are in continuous war, because the old nature has a continuing tendency to sin and rebel against God.
The Flesh (Carnality) does not produce faith but rather unbelief and defeat. It is this old flesh nature or self that war with the Spirit.
Romans 8:13 (NKJV)
For if you live according to the flesh you will die; but if by the Spirit you put to death the deeds of the body, you will live.
The born again believer does have within him contrary desires and urges. Our old nature is not yet destroyed. Our old nature constantly tries to distract us from doing the will of God and which may cause us to sin, if we are not in the spirit. To be in the spirit means to be under the controlling influence of the Holy Spirit.
Manly Christians may have a lack of true conversion and transformation in their lives, because many are being seduced by a watered down version of the gospel that doesn’t challenge them to put off the old nature, and to put on the new nature.
And how do we put on the new nature?
We put on the new nature by the destruction of the body of sin; which includes our old man, our wicked, corrupt, and fleshly self, the old nature it is to be crucified; as Christ was crucified.
We are to set our mind and affections on things that are from above. The Holy Spirit constantly wages war against our old nature. He is progressively working within us to renew us in the likeness of Christ. Even though we are a new creation, we are not totally new. We still have in us an inclination toward sin and toward evil which consists of those old characteristics or attributes which incline us toward sin. It is our old nature or old self that we still retain even though we have experienced spiritual regeneration.
Remember that we do have the indwelling Holy Spirit to help us retain our victory for we are already victorious thought Christ...
The flesh (sin) is destroyed by this quickening Spirit, that we should live unto Him who died and rose again.