There can be only one proper response to grace: a life of grateful holiness. Christ’s atoning death was “in order that the righteous requirement of the law might be fulfilled in us, who walk not according to the flesh but according to the Spirit” (Rom. 8:4).
There are two ways of understanding these words. One way is to view them as a statement of what our Lord achieved on the cross: He fulfilled what the law required by offering up a perfect obedience (the active obedience of Christ) and by meeting the law’s retribution for our sin by His death (the passive obedience of Christ). He fulfilled the righteous requirements of the law for us in His life and death.
More likely, however, Paul is stating (what he will elaborate on later in this chapter) that Christians, whose sins are forgiven, now live in holy, obedient gratitude for the grace they have received. Grateful law-keeping is the saved sinner’s response to received grace. The rest of our lives are a way of saying, “Thank you.”
Of course, salvation by grace rather than our performance can be seen as a license to sin (antinomianism). Paul’s response in Romans is something like this: if we are not tempted to think like that, we have not understood the gospel. The apostle anticipates our objection at the beginning of chapter 6: “Are we to continue in sin that grace may abound?” (Rom. 6:1).
Grace must raise the temptation to think we can sin as we please; if it does not, we have not understood the true extent of grace. However, at no time can we yield to the temptation to think this way (note Paul’s answer to his question in 6:1—“by no means”), because Christians are called to a life of holiness—holiness motivated by gratitude for all that God has done for them in the gospel of Jesus Christ.
The key to subduing the downward drag of sin in our lives is to know the impulse of gratitude that follows the experience of forgiveness and reconciliation. Law-keeping out of love is the true path of holiness.