Therefore, if anyone is in Christ, he is a new creation. The old has passed away; behold, the new has come.
It is undeniable that no one can live a perfect sinless life like Jesus. When we receive Jesus(i.e. born again), what exactly happens spiritually and physically? Our body remains the same, we are still struggling with sin(though it has reduced to some extend). What is the essence of New Creation? Is it a 'change of heart'? or 'change of character'? or 'rebirth of spirit'? How can we identify or know that something has changed? To what degree of 'change' is counted as a new creation? What is being created new here? It may be difficult to explain but attempts must have been made.
How have Mainstream Protestant denominations/theologians explained what is "New Creation"?