What is a “sin nature?”
Also known as the Old Sin Nature.
The anthropology of man was perfect in body, soul, and spirit with the first man, Adam, and also with the second Adam, our Lord Christ Jesus. Eve was made from Adam prior to the fall also perfect in body, soul, and spirit.
All other humans throughout human history inherited from Adam after the fall a separation of the spirit from the living God. This was not per God’s Plan and was due to Adam’s sin in the Garden of Eden.
Consequently, every other human being throughout human history is born with an “old sin nature”.
The old sin nature is not to be confused with propensity to perform good or evil, but instead focuses on our relationship with God.
When a human exercises faith through Christ, it is recognized as something righteous by God, who is now free through grace to regenerate our human spirit, and in this Church Age He immediately indwells the new believer in the regenerated human spirit.
The old sin nature remains in us, even as believers, influencing both our body and soul. Through faith in Christ, while we are in fellowship with Him, God then slowly begins to sanctify us, slowly changing our scarred souls and improving our heart, as we grow in Him.