"I beseech you therefore, brethren, by the mercies of God, to present your bodies a living sacrifice, holy, acceptable to God, which is your wise service." Romans 12. 1
To offer oneself as a living sacrifice is incomprehensible to the natural man, it seems unrealistic even for the Christian. It is at the same time an engagement, an obedience and something that comes from God, that God operates in us. It is something to live "according to the measure of faith that God has given to each one" (Rom 12: 3).
"To offer one's body" is not to offer external things only. But all we are, starting with our heart. This is where God speaks and pours his love. But it is also where the rebellious nature, the lie, etc., are hidden. "To offer one's body" implies the verbs "to leave, to separate, to cut". It is the dimension of repentance that allows the Kingdom of God to grow. Make room for God. Remove obstacles. The rest is God doing it.
Some of these obstacles are difficult to remove because they seem to be part of ourselves. It seems that you get used to the beams in your eyes ... There may be steps that require us to give up well-anchored but bad habits. These renunciations will earn us much more than we have "lost".
In this sacrifice of ourselves, another word is needed, it is obviously "to die". Christ died for us. He is also dead to drag us into death with him. "The death of death by death on the cross," said the Puritans. Spiritual death is the wages of sin. Death with Christ (and not only "Christ in my place" !) Is the deliverance from sin (Romans 6: 1-7). Every Christian has already lived this death at his conversion. In a more or less deep way. Later will be the reality of death "on the cross" in me, the greater will be the action of the Spirit in my life.
This living sacrifice must be lived in the greatest truth. Indeed, one can bruise the flesh for the pleasure of the flesh or think that it deserves more favor from God (1 Tim 4: 1-3) ... In this case, one deceives oneself and there is no fruit. On the contrary, it must be the work of God in me and not my work.
Source (To please the Lord)