Romans 12:1 "I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service. 2 And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God. 3 For I say, through the grace given unto me, to every man that is among you, not to think of himself more highly than he ought to think; but to think soberly, according as God hath dealt to every man the measure of faith."
Transformed is figuratively metamorphosed - the person changes: A striking alteration in appearance, character, or circumstances. (Merriam-Webster Dictionary). To clarify that change, think of the two different types. A good example is when the caterpillar turns into a butterfly - a worm (sic) turns into an beautiful thing. The change that should be obvious is when a non-Christian changes into a Christian, going from worm to butterfly symbolically. That type of change is not something concealed, but is something which is obvious.
Another term for transformed is transfigured. When one thinks of that, Jesus Christ comes to mind - the transfiguration of Jesus. Up on the mountain with God, Jesus changed!
2 Peter 1: 16 "For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were eyewitnesses of his majesty. 17 For he received from God the Father honour and glory, when there came such a voice to him from the excellent glory, This is my beloved Son, in whom I am well pleased. 18 And this voice which came from heaven we heard, when we were with him in the holy mount."Jesus somehow changed: He received honor and glory from his Father. This change is a transfiguration - A change in form or appearance : metamorphosis, or an exalting, glorifying, or spiritual change. (Merriam-Webster Dictionary). We can see from scripture the change itself:
Luke 9:29 "And as he (Jesus) prayed, the fashion of his countenance was altered, and his raiment was white and glistering... 32 But Peter and they that were with him were heavy with sleep: and when they were awake, they saw his glory."Jesus was changed, and it was both a physical and spiritual change. His countenance, or outward manner changed. Likewise, what he was wearing turned the whitest of white and glistened. This I suppose was a cleansing of the contamination of the world from his body. That leaves another change - glory. As we find from Moses conversation with God, starting in Exodus 33:19, glory is God's goodness, and God's appearance was as a shining light, so bright that eyes could not behold Him, as Ezekiel described Him.
In essence, Jesus was transfigured from the Son of Man to the Son of God. When God disappeared from the transfiguration, Jesus remained alone with those watching. My belief is that Jesus became as he would be after he died, glorified: He was endowed with all the goodness of God, the world being washed from him, not sin from him, but on him. He became the perfect sacrifice, pure and without tarnish, so that he could take on all the sins of mankind. His change was that the world was cleansed from him, and he was as he would be in heaven.
Now back to us: we are to be transformed, or transfigured if you prefer that.
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.After a person is born-again, he or she is a new person in Christ. Old things pass away, and the person is transformed into a new creature. The caterpillar - the first birth, is changed into the butterfly - the second birth. The change should be obvious! It was for Jesus, and it should be for us. Our countenance should change. Since we were washed clean, not by water, but by the spirit, we should appear to be sparkling white since we are at that instant pure. At salvation is the time that we are good - just like Jesus, because he took our sins away! Jesus transfigures us, similarly as God transfigured him!
What is the most significant difference between the once-born to the one born-again?
We should be changed, and it should show. If there is no evidence of change, it is possible that the old creature still lives, and is an imposter. The old creature merely poses as the new!
Calvinists minimize, and some even trivialize obedience to the Law of God. Those laws are the Law of Love, because the transformed creature changes from one of hate or apathy, into one who loves:
1 Peter 1:21 "Who by him do believe in God, that raised him up from the dead, and gave him glory; that your faith and hope might be in God. 22 Seeing ye have purified your souls in obeying the truth through the Spirit unto unfeigned love of the brethren, see that ye love one another with a pure heart fervently: 23 Being born again, not of corruptible seed, but of incorruptible, by the word of God, which liveth and abideth for ever."This describes the change from old creature to new - when one who has only being born once, then is born-again. The change is one of countenance - going to pure love. The way to love is to obey His commandments (John 14:15). The new creature is obedient; it is hard, but the spirit helps us. People fail God because they ignore the spirit. As Christians, we're never left to our own devices. The transformation means that the spirit lives within us.
With his transfiguration, Jesus was glorified. He received his heavenly attributes. All sin was cleansed from touching his flesh, and his body was made eternal. It was if he had already died, and as such, He and God were united. He was truly God - all goodness, who died on the cross. However, we won't be glorified until we die. Glorification is the reward for being born-again, and enduring in faith until the end.
Christians don't have to sin; it is always a choice. The transformed creature has a new beginning. We are at liberty to sin if we will to do that. The test of faith is if we choose not to sin, even though we are at liberty to sin if we want. Our countenance changes from one who takes pleasure in the world, to one who is appalled by it! If after being born-again, the Christian is still living a life of sin, without repentance, then the person has not changed - they aren't like Jesus. Then one should ask: If I have not changed, am I truly born-again?
I'll mention willingness here, but expound upon it later. Willingness is the change from old to new. It is our reasonable sacrifice: to go from unwilling to willing!
Change is our gift to Jesus for dying on the cross in our place. It is how we show our love and appreciation for him not only on Good Friday, but everyday!