Paul uses a metaphor for the Christian life in this verse: we are to be a sacrifice to God. What is unique, however, is that we are to be a “living sacrifice.” This vivid image would have been clear to anyone in ancient world since everyone has witnessed a sacrifice at some point, whether Jew or Greek. The sacrificed animal was no longer the possession of the one making the offering, but it became God’s possession. A sacrifice is a gift to a god, if we are living sacrifices, we are to be gifts wholly given over to the service of God.
To be a living sacrifice one must not “be conformed” to the world (8:2). The noun (συσχηματίζω, susxematizo) means “to be molded into another form” or perhaps guided by something else (BAGD). The pattern that Paul warns the believer to not be conformed to is the “pattern of this world,” or the lifestyle of this evil age. While the word is rare, Plutarch uses it in his essay “Virtue and Vice” (2.100f) to describe the insidious way that vice conforms itself to the attitudes of others, suppressing its own impulses to become like others.
Rather than conformed, Paul states the believer is to “be transformed.” Like the verb “conformed,” the word μεταμορφόω (metamorfoo) can refer to both outward physical changes (such as the transfiguration, Matt 17:2) and inward spiritual changes (BAGD). It is used of the change of the physical body in glory (2 Cor 3:18.) But here in Romans 12:2 it means an inward spiritual change of the believer by the power of the spirit.
The key to this metamorphosis is the “renewing” of our minds. I think that Paul is saying that the one who is in Christ is in fact a new creation (2 Cor 5:20), but that this new creation is an ongoing process, leaving behind one world-view and changing our thinking to conform to a new world-view. Thinking back to the situation in Corinth, the church did not seem to have embraced this change in thinking. They still were “conformed” to the pattern of this world and had not progressed very far in “being transformed” by the renewing of their minds. They still thought like the world. But here Paul says that the one who is a living sacrifice thinks differently, and therefore is different from the “pattern of this world.”
I think that perhaps this is what is wrong with a great deal of what passes for Christian thinking these days. There is a tendency to adopt secular business principles and put a thin veneer of Christianity on then, somehow making then acceptable for organizing the Church and doing ministry. My local Christian book store has piles of books with titles like Seven Principles for Church Leadership which are standard leadership material drawn from corporate American, illustrated with a Bible story (usually with a Sunday School understanding of the text cited!) This is not transformed thinking, but worldly thinking masquerading as biblical principles.
What would the church look like if it was really composed of people who had been “transformed by the renewing of their minds”?