"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." (Romans 12:2)
In Mere Christianity, C.S. Lewis reminds us that "He [Jesus] warned people to 'count the cost' before becoming Christians. 'Make no mistake," He says, 'if you let me, I will make you perfect. The moment you put yourself in My hands, that is what you are in for. Nothing less, or other, than that." Paul tells us in Romans 8:29, we were actually "predestinated" to be conformed to the image of Christ. If we are one of His, He is going to make sure that we end up exactly as He wants us to be.
That being said, unfortunately, the world is trying to conform us to their standards, as well. Pretty uncomfortable quarters, huh? In fact, the word "conformed" comes from a word that means to be "squeezed in." That pretty well describes the situation. As believers, we are recipients of a new "divine nature" (2 Pet. 1:4) that has taken up residence with an old, sinful one (Eph.2:3, that is fighting eviction, tooth and toenail. Oh, the new one will win; we can be sure of that. But are we also predestinated to have the life squeezed out of us, in the meantime? I don't think so.
The world, like God, is capable of conforming us to its image; but the ability to transform—from the inside out—is exclusively held by God. Transformation (literally, "metamorphosis") changes the whole mindset, as the verse indicates. It predisposes us toward God and away from evil. It does not mean we cannot be seduced by Satan; but it does mean, when we are, it will go against our true, new nature. That's why, as Charles Spurgeon said, a Christian never sins successfully. It may look like a coup, but will end up being a collapse. It never turns out the way we thought it would.
As you and I struggle against the world, the flesh, and the devil, we should remember that our Lord fought that fight, too. He prevailed, and so may we. We have been transformed, by grace, into the children of God, "created unto good works"; and as we allow Him to renew our minds through His Word, we are being conformed into the image of His Son.
Conformed or transformed? Both, praise God!