The old nature is a product of our environment and upbringing, contact with a worldly system of values, and our learned behaviors. We take on board negative experiences and traumatic occasions and treat them as though they are the truth about us for all of time.
The old self, until it is replaced in our experience, carries some weight in our personality. It supplies the head-noise, the background tape that runs on a loop incessantly in our thinking. All stress is already on that tape. When situations arise that are difficult for us, the button gets pressed and the old messages about ourselves get played. Stress is the result.
The new nature is a product of Heaven, not of your doing.
It is the way that God thinks about us in Christ. He has nothing but approval for us because that’s why He put us into Christ in the first place—so that we could always be accepted in the Beloved (Ephesians 1:6).
The Lord has a way of thinking about us that builds us up, empowers us to grow, and causes us to be constantly renewed in the Spirit. We need never lose heart because our outer man (old self ) is being killed off, when our inner man (our true self in Jesus) is being renewed day by day (2 Corinthians 4:16).
Each day, in Christ, we are practicing the joyful discipline of being renewed in the spirit of our mind (Ephesians 4:23). That means we are enabling our thinking to come from a source that is full of love for us and wants to see become more of who Jesus is for us.
The new man hears a heart voice, not old head-noise.
We have put on a new self which is renewed in a true knowledge according to the image of the One who created him (Colossians 3:10). The true knowledge is that our head-noise belongs to the old man, crucified in Christ, and our new inner voice is made in the image of Jesus. We can only ever be fully transformed by the renewing of our mind (Romans 12:2).
P.S. Get more materials on this new heart voice and how to build your life around it here.