I was reading a book whose authors contend that Christians being "not under law, but under grace" (Romans 6:14–15) and their being "dead to the law" (Romans 7:4–6) shouldn't be taken to mean that Christians aren't under obligation to the Law. Their explanation is that "not under law" means not justified by keeping the law.
This view isn't as uncommon as we might expect, so it's worth thinking over.
Galatians 4:3–5 asserts that Christ came to "redeem those under law". So we can confidently say that at least some people are (or were) "under law". If we are to take these authors' view of what it means to be "under law", then we have to conclude that Galatians 4:3–5 teaches there are those who are justified by works. That's an odd statement in light of Galatians 3:10–12, Romans 3:19–20, etc.
What the epistles explicitly teach is that God has only ever justified sinners on the basis of faith (Romans 1:17, 4:1–15). God has never justified on the basis of works – not based on the Law of Moses or any other law. Justification is by faith, only and always. This is the clear teaching of the first four chapters of Romans, as well as the epistle to the Galatians.
So what does it mean to be "under the law"? Romans and Galatians both make it clear that the function of the Law was to reveal sin (not, as Darby points out, sins). In fact, Galatians makes the astonishing statement that it would have been unrighteous of God to add the Law as a condition to a promise He had made to Abraham 400 years earlier (Galatians 3:15–26). We can't make a promise, then add caveats and conditions long after the fact. So we conclude that the Law has nothing – nothing! – to do with justification in God's sight, nor even with the promised blessing to Abraham.
So the Law was only ever a "rule of life", never a means of justification.
And at this point, the entire argument falls apart. If the Law was never more than a rule of life, then it cannot be said that those "under the Law" were under it as more than a rule of life. Nor can it be said that those "not under Law" are under it as a rule of life, but not as a means of justification. That's absurd.
It's striking that Romans 7:4–6 describes our relationship to the Law in the same terms that Romans 6:11 uses to describe our relationship to sin. The Christian lives as separately from the Law as he does from sin.
Now, I realize there are more nuanced views that I've sort of glossed over here. But it seems to me that the Epistles clearly and unequivocally teach that the believer is, indeed, dead to the Law and under no obligation to it. That doesn't mean the believer is to live lawlessly, not at all! But it falls far short of what Scripture teaches to suggest that the Law has any authority at all over the believer.