Paul in Romans 12:1-2 exhorts us to holy living by presenting our bodies as living sacrifices to God. " I appeal to you therefore, brothers, by the mercies of God, to present your bodies as a living sacrifice, holy and acceptable to God, which is your spiritual worship".
It is interesting that the word for sacrifice here is never used in terms of a animal sacrifice in the Hebrew Old Testament. It is instead used of the priests service in standing before the Lord. The verb form used is a point action ( a one time deal ). His idea here then implies that there be one definite presentation. It could only mean your first repentance and commitment toward God, but with continuing implications. There are times to renew such a commitment, but not to repeat it. It follows the idea of progressive sanctification; "taking up your cross daily and following Him". Its not the passive idea of surrender either, by giving up your life only because God is stronger and bigger than yourself, like giving up a battle between you and God, or even the idea of yielding. You present your bodies as a gift, as you would to a friend. Like a gift to a friend you offer the whole thing and not keep parts of it to yourself. The commitment you offer to God is your whole body, not just "yourselves". The body is an outward expression and form of the inner person; it includes all your talents, abilities, desires, and aspirations. Just like your spirit, God created your outward bodies as well, and you should present your outward bodies like you would your inner self before God as well. All should be given to God.
The talents, abilities, and characteristics we have, he gave us. He has made us fit for His service. If God has made us for His service, then our service is to do his will. Those who are redeemed and filled with gratitude, for the gift the God gives us in return ( grace and mercy ), will desire to please God. This dedication involves direction or else it delusion. It has to be directed to God's will for it to be pleasing before the Lord. This dedication also involves renewal like I mentioned above. One example of renewal is in the observance of communion, " in the memory of Him". Every time we have communion, it is an act of faith by which we confirm that we have entered into the covenant with God and are awaiting the fulfillment of the promise, and it is an act of commitment whereby we reaffirm our obligations and commitment to serve him as his people.
So the start of this this spiritual living is the serious commitment and dedication to the Lord, not just an emotional response, where people don't really know what it all means. This commitment while may be made from an emotional response, ultimately comes with the beginning of spiritual growth. When believers learn more about God and Christ, salvation, the covenant responsibilities, and the mission of the Church, and all that it means to be a follower of Christ then they are ready to make that true commitment to each and everyday " take up their cross".
The second verse here: Do not be conformed to this world, but be transformed by the renewing by the renewal of your mind, that by testing you may discern what is the will of God, what is good and acceptable and perfect.", deals with our relationship to the world. Paul is saying not to take as a way of living the present, foolish, fashions of the world, its dominance in evil motives and moods. He is urging us toward true biblical separation, to be " set apart from the world". He is urging what Christ expressed in John 18:36 " My kingdom is not of this world". Separation from the world is not to be reduced to a few logistical, legalistic, do and don'ts; it is wisdom to live squeaky clean in a world that is dominated and dirty from selfishness, greed, pleasure, and indifference to the needs of others. We are not to be actors, conforming to this present world, but to be genuine, because the Spirit of truth is working within us. If we let the attitude of the world dominate our lives, then we constitute worldliness. If our thinking and way of life matches that of someone who is not a believer; if we live, love and make decisions as the world does, to the exclusion of Christ, then we are conformed to the world. That way of living cannot harmonize with the dedication and sanctification of the spiritual life.
Christians today and in America come close to being caught up in worldliness. Little things begin to change our way of thinking. For example, people crave a blessing from God, meaning success, wealth, security. But we have forgotten that we must first be a blessing in the world for God to bless us, and God may not bless us with stuff that we think we need such as material things. Or, people pray earnestly for illnesses and diseases to be removed, or instead of praying they think they can command them to leave; and it is perfectly understandable that people should want to be free from the pain and suffering. But they have forgotten that when they suffer they are to count it all joy, because it gives them an opportunity to use that suffering for the glory of God, as a witness to the world. They need to add to their prayers that God will change them spiritually and use them. These trends and many more show that many in the Church have bought into the worldliness and materialism of this country, and it is hindering the Church from being a true witness for the Lord and a compassionate help of people in great need.
But sanctification is not just being separated from the world, with a list of worldly things that one should not do; it is a positive transformation by which we become more and more like Jesus Christ which is accomplished: “by the renewing of your mind.” One renews the mind by sacrificing it, along with the entire body to the worship and work of the Holy Spirit and studying God Word day by day. Then one becomes closer to the mind and will of Christ, the life begins to change from carnality to glory as we reflect, as in a mirror, the glory of the Lord revealed in Scripture. Too many Christians rely on to much on personal experiences to get them through the week, perhaps an uplifting service, or a supernatural feeling and do not study the Word. They have forgotten that God redeemed the mind, as well as the heart.
So the essentials of spiritual growth are: dedication, separation (from the world and to God), and transformation by the renewing of the mind. Once this begins to develop, we will be able to test and approve what the will of God is.