Therefore, if anyone is in Christ, he is a new creation; old things have passed away; behold, all things have become new. 2 Corinthians 5:17 (NKJ)
If a dog could somehow be miraculously changed into a man he would be a new creation with a whole new nature! The funny movie called the Shaggy Dog from Disney illustrates for us what many Christians believe about themselves. Someday they could slide back into being a sinful lost dog, then change back into a born again [man] believer on another day.
This illustration is simple and straight forward to comprehend. As incredible and impossible as this would be, it is exactly what is meant in scripture when describing the change that takes place in a true born again experience. When someone is converted, born again, the nature changes inside a man because God’s Spirit actually moves inside him and he is overwhelmed with a new nature, God himself.
But you do not change back and forth like the movie.
Jesus explains this in John 3 (NKJ): “Most assuredly, I say to you, unless one is born again, he cannot see the kingdom of God.”
Nicodemus said to Him, “How can a man be born when he is old? Can he enter a second time into his mother’s womb and be born?” Jesus answered, “Most assuredly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God. That which is born of the flesh is flesh, and that which is born of the Spirit is spirit. Do not marvel that I said to you, ‘You must be born again.’“
This is what Ezekiel the prophet proclaimed many, many years before to Israel. “And I will give you a new heart, and I will put a new spirit in you. I will take out your stony, stubborn heart and give you a tender, responsive heart. And I will put my Spirit in you so that you will follow my decrees and be careful to obey my regulations.” Ezekiel 36:26-27 (NLT)
Now Jesus did not leave the discussion yet. He made sure that we could see in our lives what He meant in the everyday. Remember the dog illustration. If you knew the dog and watched the transformation you would see clear and unarguable change. When your old dog started talking in English you would hear change. When he could not bark anymore you would have evidence. When he ate differently, looked differently, and so on, you could clearly measure or count the changes. A complete nature change would take place. Dog nature to human nature.
Even though God is invisible to our eyes, we are told what changes we can see in salvation. We are told what we are to look for, so that we know whether we are changed with God inside us. And it is simple. We and everybody else can see God’s nature coming out of us.
Jesus explains this with the illustration of the wind. “The wind blows where it wishes, and you hear the sound of it, but cannot tell where it comes from and where it goes. So is everyone who is born of the Spirit.” John 3:8 (NKJ)
Air is invisible. The wind blows and you can feel and see the results and evidence of the invisible air. The trees move, the clouds are pushed across the sky, and you feel the pressure across your body. Jesus says this is exactly what happens when the Spirit of God invades people. Evidence of God shows up in people by changing their lives. People are changed from within their hearts.
God loves without reservation and desire of anything in return. People love conditionally and demand kindness returned.
God never lies, steals, breaks His word, is unjust, and so on. People are so self centered that they lie when it gives them advantage or a reward, steal if it is an easy way to accomplish their desires, break their promises when it doesn’t please them to continue, unfair as long it strengthens themselves, focus on their own selfish kingdom building, bank account filling, and pleasure seeking without changing direction.
God describes it like this in Romans 3:
“As it is written: There is none righteous, no, not one;
11 There is none who understands;
There is none who seeks after God.
12 They have all turned aside;
They have together become unprofitable;
There is none who does good, no, not one.”
13 “Their throat is an open tomb;
With their tongues they have practiced deceit”;
“The poison of asps is under their lips”;
14 “Whose mouth is full of cursing and bitterness.”
15 “Their feet are swift to shed blood;
16 Destruction and misery are in their ways;
17 And the way of peace they have not known.”
“There is no fear of God before their eyes.”
Paul also explains this fruitless sin nature working inside sinful man as follows: “For what I am doing, I do not understand. For what I will to do, that I do not practice; but what I hate, that I do.” Romans 7:15
You will gain the knowledge of God’s laws from reading the Bible and going to church. Paul first learned the truth of sin as a faithful Jew, but it did not transform him. It convinced him of being a sinner and failure. It convicted him of how unworthy he was before a holy God.
Paul pours out this simple explanation of what the Spirit of God does inside a born again Christian.
Romans 8:1-16 (NLT)
1 So now there is no condemnation for those who belong to Christ Jesus.
2 And because you belong to him, the power of the life-giving Spirit has freed you from the power of sin that leads to death.
3 The law of Moses was unable to save us because of the weakness of our sinful nature. So God did what the law could not do. He sent his own Son in a body like the bodies we sinners have. And in that body God declared an end to sin’s control over us by giving his Son as a sacrifice for our sins.
4 He did this so that the just requirement of the law would be fully satisfied for us, who no longer follow our sinful nature but instead follow the Spirit.
5 Those who are dominated by the sinful nature think about sinful things, but those who are controlled by the Holy Spirit think about things that please the Spirit.
6 So letting your sinful nature control your mind leads to death. But letting the Spirit control your mind leads to life and peace.
7 For the sinful nature is always hostile to God. It never did obey God’s laws, and it never will.
8 That’s why those who are still under the control of their sinful nature can never please God.
9 But you are not controlled by your sinful nature. You are controlled by the Spirit if you have the Spirit of God living in you. (And remember that those who do not have the Spirit of Christ living in them do not belong to him at all.)
10 And Christ lives within you, so even though your body will die because of sin, the Spirit gives you life because you have been made right with God.
11 The Spirit of God, who raised Jesus from the dead, lives in you. And just as God raised Christ Jesus from the dead, he will give life to your mortal bodies by this same Spirit living within you.
12 Therefore, dear brothers and sisters, you have no obligation to do what your sinful nature urges you to do.
13 For if you live by its dictates, you will die. But if through the power of the Spirit you put to death the deeds of your sinful nature, you will live.
14 For all who are led by the Spirit of God are children of God.
15 So you have not received a spirit that makes you fearful slaves. Instead, you received God’s Spirit when he adopted you as his own children. Now we call him, “Abba, Father.”
16 For his Spirit joins with our spirit to affirm that we are God’s children.
The changes are evident. The Christian changes in desire and ability, doing good according to what God says is good in the Bible. Life changes as real as if a dog actually became a man. “We know that we have passed from death unto life, because we love the brethren. He who does not love his brother abides in death [still a dog].” 1 John 3:14
If a person doesn’t change friendships and love being in church with church people, he is still not a born again believer.
Here’s another change, “Whoever commits sin also commits lawlessness, and sin is lawlessness.” 1 John 3:4 The person who keeps disobeying God’s commands in the Bible, whether he attends church or not, is not a new man, but still an old dog. Whoever is changed in nature from a dog to a new man “does not sin.” [verse 6] “He who sins is of the devil… whoever is born of God does not sin, for His seed remains in him; and he cannot sin, because he has been born of God.” There is no changing back from man to dog!
The change of nature is so permanent that the Bible explains the reason some seem to go back and fall away, backslide, or lose their salvation. “Little children, it is the last hour; and as you have heard that the Antichrist is coming, even now many antichrists have come, by which we know that it is the last hour. They went out from us, but they were not of us; for if they had been of us, they would have continued with us; but they went out that they might be made manifest, that none of them were of us.” [1 John 2:18,19]
If you see people leaving the church, going into sinful, selfish life styles it is not because they changed back to a dog. They were still a dog inside when you met them, and you did not realize it. John makes it clear with his words just quoted. An example of this is even given with the twelve apostles of Jesus.
Remember when Jesus told his disciples that one would betray him. No one jumped up and said, “Yea, it’s Judas!” But did you know he was a devil from the beginning according John, but he appeared like all the other disciples?
His greed was not painted on his forehead, but in his heart. He was the treasurer of the group and held the purse. Jesus was well aware of his sinful lost condition, but not the naive followers. Speaking of Judas John says, “This he said, not that he cared for the poor, but because he was a thief, and had the money box; and he used to take what was put in it.” [John 12:6] He was a sneaky thief, the others did not know about his persistent law breaking.
And John 6:70-71 reads: “Jesus answered them, ‘Did I not choose you, the twelve, and one of you is a devil?‘ He spoke of Judas Iscariot, the son of Simon, for it was he who would betray Him, being one of the twelve.”
If they were not new disciples themselves they would have been able to see the fruit of the old dog as he was. But they had a lot of maturing before they could see the dangerous dogs that sneak into the ranks of the believers. That discernment came later. [Acts 17; Jude; and 2 Peter are examples]
Since it is hard to “judge” someone without being condemned for judging, most people look away when people don’t seem to be right. But Jesus told us to be fruit inspectors in Matthew 7. “You will know them by their fruits… Not everyone who says to Me, ’Lord, Lord,’ shall enter the kingdom of heaven, but he who does the will of My Father in heaven… And then I will declare to them, ’I never knew you; depart from Me, you who practice lawlessness.’”
Many of the most convincing “Christians” that do believe in Jesus and think they are going to heaven will be turned away because they never stopped their disobedience by becoming new natured men, but instead are still dog natured men, proven by practicing disobedience to God‘s law. Just like Judas they secretly practice immorality, greed, or one of the many possible sins and even convince themselves they are okay before God because no one is perfect.
Now one last thing. Maturity takes a lifetime, but repentance from a sinful life demands short term results. Paul made this clear in his two books called 1 and 2 Corinthians. In the first book he corrected them over many sinful actions and attitudes and expected change. By the end of his 2nd book he says, “Examine yourselves as to whether you are in the faith. Prove yourselves…” [13:5].
It was between 1-2 years between these two letters to the church of Corinth in Greece. Enough time had passed and if no change was made he challenged them to prove whether they were born again or not. The new born again nature is not hidden for a long time, the new nature comes out in the fruit of the Spirit. Paul demanded fruit from his converts. God does too. Read Galatians 5:16-26.
For further understandind see the 7 evidences of salvation here.