To live a free life pleasing to God, we must have renewed minds. To live in heaven forever, we must acquire a fresh, spiritual way of thinking (Eph 4:23) and take on the mind of Christ (1 Cor 2:16).
However, before our minds become renewed, our bodies must be sacrificed to God (Rm 12:1). Jesus bought our bodies at the price of His death on the cross (1 Cor 6:19-20), so, when we offer our bodies to Him as living sacrifices, we acknowledge His ownership of them. This means that all parts of our bodies become weapons for justice (Rm 6:13). When we sacrifice our bodies to God, we discipline and master them (1 Cor 9:27). We fast frequently, do bodily penance, and fill up in our bodies what is lacking in the sufferings of Christ (Col 1:24).
Through our sacrificed bodies, God transforms our minds. Finally, through our transformed minds, our sacrificed bodies become transformed themselves. When Jesus comes a final time, "He will give a new form to this lowly body of ours and remake it according to the pattern of His glorified body" (Phil 3:21). This wonderful, and eventually total, transformation of mind and body begins with the offering of our bodies to God. Therefore, "I beg you through the mercy of God to offer your bodies as a living sacrifice holy and acceptable to God" (Rm 12:1).