The duty of believers is “to present their bodies to God as a living sacrifice, holy and acceptable to him,” and in this consists the lawful worship of him (Rom 12:1). From this is derived the basis of the exhortation that “they be not conformed to the fashion of this world, but be transformed by the renewal of their minds, so that they may prove what is the will of God” (Rom 12:2). Now the great thing is this: we are consecrated and dedicated to God in order that we may thereafter think, speak, meditate, and do, nothing except to his glory. For a sacred thing may not be applied to profane uses without marked injury to him.
If we, then, are not our own (cf. 1 Cor 6:19) but the Lord’s, it is clear what error we must flee, and whither we must direct all the acts of our life.
We are not our own: let not our reason nor our will, therefore, sway our plans and deeds. We are not our own: let us therefore not set it as our goal to seek what is expedient for us according to the flesh. We are not our own: in so far as we can, let us therefore forget ourselves and all that is ours.
Conversely, we are God’s: let us therefore live for him and die for him. We are God’s: let his wisdom and will therefore rule all our actions. We are God’s: let all the parts of our life accordingly strive toward him as our only lawful goal (Rom 14:8; cf. 1 Cor 6:19). O, how much has that man profited who, having been taught that he is not his own, has taken away dominion and rule from his own reason that he may yield it to God! For, as consulting our self-interest is the pestilence that most effectively leads to our destruction, so the sole haven of salvation is to be wise in nothing and to will nothing through ourselves but to follow the leading of the Lord alone.
Institutes of the Christian Religion, 3.7.1.