The “Old man" and the "New man" are examples used by the Apostle Paul, in his letters to the Ephesians and Colossians.

Ephesians 4:22-24 

“You were taught, with regard to your former way of life, to put off your old self, which is being corrupted by its deceitful desires, to be made new in the attitude of your minds; and to put on the new self, created to be like God in true righteousness and holiness.”

Colossians 3:9-10

“Do not lie to each other, since you have taken off your old self with its practices and have put on the new self, which is being renewed in knowledge in the image of its Creator.”

These examples describe two distinct ways of life associated with a relationship with God.

The "Old man" refers to the former way of life or the Old nature,

associated with a person being dead in their trespasses and sins, hostile to God, and destined to wrath. 

The “New man" represents the new life or New nature, that is created after the likeness of God.

This New self is true Righteousness and Holiness, created through Grace and Faith.

It’s another example of God’s love for His creation.

Believers are taught to "put off" the corrupted Old self, which belongs to their former way of life , and “put on” the incorruptible, the New self, which is created in the likeness of God.

Galatians 5:22

“But the fruit of the Spirit is love, joy, peace, forbearance, kindness, goodness, faithfulness, gentleness and self-control."

The fruit of the Spirit, achieved by the Holy Spirit influencing our thoughts, feelings, and actions, through living the new way, by changing our thinking and acting that reflects God's likeness.