These verses speak to the "reasonable service" that is expected of every Believer in Jesus Christ. Our lives need to become living sacrifices so that Jesus Christ can be manifested to the world through us. After all, the world doesn't need you or me, but it does need Jesus! And people are never going to be open to accepting Jesus until we start showing to the world that Christians -- Bible-believing Christians -- really have found true life. By doing this we're letting the light of Life shine forth for all to see!
So what are we actually sacrificing? Our old selves and the old way of life. Your testimony will take on a whole new level of meaning when your life starts lining up with the message that you share with others. There's no bigger hypocrite than the "Christian" who talks the talk but isn't walking the walk. Why would anyone want what that "Christian" has if all it amounts to is empty words with no discernible change in life style? Let go of all the things that are of the world and start embracing the things that will last forever and people will notice that there's something different about you.
Notice that we're to be "holy" which means to be separated from the world. We're not talking about legalism. We're talking about living now as if we're already in heaven. That's the only way the world will ever believe that we're serious about our faith. It's that attitude of being obedient to God's Word out of love for Him that God finds acceptable. Let go of anything that has a hold on you. Forsake it and turn away from it. Are you grateful to Jesus for saving you? Then live your life to please Him.
Notice that Paul refers to this as our "reasonable" service. I would have to agree. After all, the Father gave up His only begotten Son as part of His plan of redemption. Jesus gave up glory, took on a human nature, then laid His perfect life down to pay the eternal price that nobody but Jesus Himself could pay. Now all He wants is for us to model His life so that others can also be brought into the Kingdom. Let go of the world and embrace the new life. It's a very small price to pay.
In verse 2, Paul gives us two active commands: 1) "Be not conformed to this world" and 2) "Be ye transformed by the renewing of your mind."
The Holy Spirit makes it clear through Paul's words that we need to keep ourselves from being conformed to the world. This makes perfect sense as the world is an enemy of God (James 4:4). The world wants anything BUT God. Oh, the world can seem to put on a pretty good act sometimes, pretending to be open to God. But start preaching Jesus as the only Way to heaven (Johyn 14:6) and the world will bring its fury down on you. And when I mention the world, I'm referring to religion as well. Religion can't make us right with the Father. If it could, Jesus wouldn't have had to go to the cross.
Instead of conforming to the world, we're to be transformed by the renewing of our minds. Even that isn't a task that belongs to us entirely; the Holy Spirit will truly enable us to be transformed (of course, I'm writing this to born-again believers as the Holy Spirit only dwells inside believers). Still, it's up to us to make the prayerful and willful decision to stop living as the world does and start living as God desires. So how do we do this?
There are two primary ways: Bible study and prayer. Bible study means opening up God's Word and digging into it. Don't just read through it. Slow down. Ask the Lord questions about what you're reading and then look for the answers He'll provide. God loves it when we learn to feast on His Word. The more you do it, the more you'll learn about Him and the closer you'll be able to get to Him. And in the process of asking Him questions, we're also engaging in prayer to Him.
People often wonder how to pray. The best way to learn is to study God's Word, look for promises He makes then ask Him to make good on those promises in your life or in the lives of those around you. I'm not talking about "prosperity" thoughts as far as they concern earthly things, but I am talking about asking God to prosper you in your walk in the Spirit. Study the many prayers of the saints that have been recorded for us then apply what you learn to your own prayer life.
Finally, notice that Pauls' two commands in verse 2 are part of a cause and effect process: when we stop conforming to the world and prayerfully seek to be transformed by the renewing of our minds, our lives become a living proof that God's will is "good, and acceptable, and perfect." In other words, when we do what Paul calls us to do, we won't just tell people about Jesus we'll show them Jesus by letting His life shine through us. We become walking, talking proof that God can indeed transform any man, woman or child who puts their faith in Jesus.
If you've ever had problems convincing someone that Jesus is the answer, maybe the only real problem is that your life hasn't become the proof that someone needs. Let Jesus shine forth through you and people will take notice.