Scripture normally divides all humans into two classes;
The Natural man ( in the Greek= Psuckikos-)
The Spiritual man ( in the Greek-Pneumatikos)
We understand by scripture that the Natural man does not accept the things of the Spirit of God;
To him they are foolishness.
He does not and cannot accept them because they are spiritually discernsd. 1 Cor 2:14
The Spiritual man is Regenerate and does have the Holy Spirit dwelling in him; (Romans 5:5 ; John 14:16-17)
The Spiritual man has a New Nature
Now here are the questions;
What happens to the Old Nature when a person becomes Born-Again?
Does he retain that old Nature and if he does, how does he get rid of it?
What happens to his old way of thinking and why does he have to renew his mind?
Wasn't that part of the old things that were passed away?
What was Paul speaking of when he said, 'Old Things are passed away?