I I Corinthians 5:17 Therefore if any man be in Christ, he is a new creature: old things are passed away; behold all things are become new. Galatians 6:15 For in Christ Jesus neither circumcision availeth anything, nor uncircumcision, but a new creature.
Many new translations will change creature to creation in these texts. You may ask what is the difference? This is a point of doctrine we will attempt to explain. Now when I got saved in 1979 I was a short white male with blue eyes and dark curly hair. After I got saved I was still a short white male with blue eyes and dark curly hair. I was not a new creation but praise the Lord I was a new creature! The change was on the inside, I was born again, I had new desires and a new destiny. My soul was circumcised from my flesh, my spirit was renewed and Christ by means of the Holy Spirit took up permanent dwelling in my heart. I was able to understand and enjoy the Bible with out man’s help because God Himself was teaching me.
Now as to the doctrinal importance. By the way doctrine is not a bad word. Doctrine and doctrines is found 56 times in the Bible. The Jehovah Witness and Seventh Day Adventists teach that the body and soul are the same thing and that when the body dies you cease to exist until the resurrection when God recreates you from his memory. That will work if you are a new creation rather than a new creature. But as you see in I Thessalonians 5:23 the soul is not the body nor is the soul the spirit. After you die the soul goes to Heaven or Hell and stays there forever. Yes one little change like this can affect vast areas of truth and lead people to deny a basic fact of God Almighty and his judgement.