This sermon is from Romans 12:1-8.  First and foremost, a Christian is one who worships God.  This worship does not merely take place on Sunday mornings when Christians sing together, but in light of the mercies of God seen in the gospel (Romans 1-11), worship should be the aim of every Christian at all times by presenting our bodies as a living sacrifice.  Christians worship in this way when we are transformed by the renewal of our minds (v.2) and when we come together and use our gifts for the building up of the body of Christ (v.3-8).