2 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.
2 Corinthians 5:21 For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him.
The spiritual change happens at the conversion is when we accept the great gift from God all of our sins are put onto Jesus and attributed to Him and His work on the cross, and He by grace gives us His righteousness. It does not stop there though, and this spiritual change shows up in our day to day lives.
There is a Spiritual change that shows in our lives, thoughts and actions. I remember reading a story about a lady speaking with Charles Spurgeon about being a Christian. She said she said she could never be a Christian because she enjoyed playing card games, the occasional sherry, and going to the theater and could never give them up to which Charles replied “I play all the cards I want to, drink all I want to, and go to the theater as much as I want to.”
“Really!” the lady replied. “Yes, but I do not want to!” said the great preacher. To me that is a real sighn of conversion, of the changed life: God changes our “wanter.”
I remember when God saved me. That night I was at home, got up and stubbed my little toe on a table. Instantly the old nature showed up in me as I started with a stream of “blankety-blanks” (fill in the blanks) and almost immediately I pulled up and stopped like I had been slapped with this thought: “Is this why I saved you?” I immediately repented and my first memory verse became 2 Timothy 2:16 (But shun profane and vain babblings: for they will increase unto more ungodliness.)
The conversion comes right away, but growth comes over time. We are given the righteousness of Jesus and the fruit of that will show in our lives as we grow and live the life. We walk the walk, when we are converted we have a conversation, a walk, a new way of life.
As the old saying goes “the proof is in the pudding” and if we do not walk after righteousness, if we live in willful and unrepentant sin, then there is a consiquence:
Hebrews 12:5-8 And ye have forgotten the exhortation which speaketh unto you as unto children, My son, despise not thou the chastening of the Lord, nor faint when thou art rebuked of him: (6) For whom the Lord loveth he chasteneth, and scourgeth every son whom he receiveth. (7) If ye endure chastening, God dealeth with you as with sons; for what son is he whom the father chasteneth not? (8) But if ye be without chastisement, whereof all are partakers, then are ye bastards, and not sons.
If we live in willful rebellion and God does not intervene, does not chastise, then the whole process comes under question and we need to reexamine our salvation, because then we are bastards (illegitimate children) and not really sons of God.