Being transformed and changed in this way is what the Bible calls "repentance." The word repent means "to turn." The change is so drastic, that Jesus calls it being "born again (John 3:3). Jesus taught that In order to be saved, one must be born again. If not, they will never enter into God's kingdom and be lost. The Apostle Paul says it like this, "Therefore I urge you, brethren, by the mercies of God, to present your bodies a living and holy sacrifice, acceptable to God, which is your spiritual service of worship. And do not be conformed to this world, but be transformed by the renewing of your mind, so that you may discern what the will of God is, that which is good and acceptable and perfect (Rom 12:1-2)." The change that is to happen to us is so radical, that Paul says we are to be "living sacrifices." This means we sacrifice our own selfish desires and live according to God's desires. It involves a renewing of our mind, changing the way we think. We consider all things from God's perspective according to his word. This is why refers to baptism as being baptism "into death (Rom 6:1-7)." In our baptism, we are dying to ourselves and coming up out of the water as a new person.
There is a different message for those who have already been saved. For those who are being transformed into the image of God, Jesus said, "As the Father has sent Me, I also send you (John 20:21)." Just as Jesus came bearing the image of God so that we could "see his glory (John 1:14)," and imitate him, Jesus now sends us into the world to bear his image. A "visual sermon" has much more impact than a radio program or tract, and you are that visual sermon as you, transformed by the Spirit, bear the image of the Heavenly in your actions and your speech. The Apostle Paul puts it this way,
"Now all these things are from God, who reconciled us to Himself through Christ and gave us the ministry of reconciliation, namely, that God was in Christ reconciling the world to Himself, not counting their trespasses against them, and He has committed to us the word of reconciliation. Therefore, we are ambassadors for Christ, as though God were making an appeal through us; we beg you on behalf of Christ, be reconciled to God (2 Cor 5:18-20)."