In the Old Testament, sacrifice meant that a life had to be taken. This points to the life and death of Jesus Christ, which in a sense had to be taken in order for us to be united with God.
Paul thought about the sacrifice that our Lord made when he writes about our response to it: sacrificing ourselves.
1 Therefore, I urge you, brothers and sisters, in view of God’s mercy, to offer your bodies as a living sacrifice, holy and pleasing to God—this is your true and proper worship. 2 Do not conform to the pattern of this world, but be transformed by the renewing of your mind. Then you will be able to test and approve what God’s will is—his good, pleasing and perfect will.
3 For by the grace given me I say to every one of you: Do not think of yourself more highly than you ought, but rather think of yourself with sober judgment, in accordance with the faith God has distributed to each of you. 4 For just as each of us has one body with many members, and these members do not all have the same function, 5 so in Christ we, though many, form one body, and each member belongs to all the others. 6 We have different gifts, according to the grace given to each of us. If your gift is prophesying, then prophesy in accordance with your faith; 7 if it is serving, then serve; if it is teaching, then teach; 8 if it is to encourage, then give encouragement; if it is giving, then give generously; if it is to lead, do it diligently; if it is to show mercy, do it cheerfully.
Romans 12:1-8 (NIV)
In this passage, it is not about a sacrifice on an altar or a on cross. It is about the sacrifice of being in His service. It is a sacrifice as an act of worship for the living God. Paul calls it the true worship.
In order to make this sacrifice, it is necessary that we change (verse 2). Living life in this world is very different from living a life in the Kingdom of Heaven. We should not conform to this world, but should be transformed. We need a new state of mind. It is only then that we discover (by praying, reading the Bible, interacting with fellow Christians) what God’s will is, what pleases Him, and what He wants us to do.
If we are lukewarm, by not really conforming to this world nor conforming to Him either, we will still be influenced by this world. And that will change us. But the life of a Christian should not be changed passively by everything that we are confronted with in this world. Rather, we should be actively changed by accepting the transformation that God gives! Ask Him to change your state of mind.
God has given us guidelines as to how we may live a life for Him. He wants us to live a life, according to the faith He has given us (verse 6). This is not the faith by which we were saved. This is the faith through which we can trust Him to do things in our lives that we could not do ourselves. Do you believe that God can change you? Do you believe that God can transform your mind? Do you believe that your life is precious to God, and that He wants you to sacrifice your life for Him, so that you can be in His service?
When our life is renewed, and when we can stretch out through the faith we have received, it is usable for the King. The fact that He can use us means that we may serve others, as well, with the gifts (received from Him) that will help us do so (verse 4-8). We have all received different gifts, and we perform different tasks. We should perform those tasks, in accordance to our faith; we do not have to do something we really cannot oversee. And as our faith grows, so do our sacrifices to Him by serving Him in new ways.
A life like described above, serves Him, and serves His children in His church. Therefore, reach for the talents and gifts He wants to grant you. Have faith, and step out, so that His church will be served and built. In that way, His light will shine in this world.