I have paraphrased the question(s) below:
If the Decalogue is
technically defunct in the New Covenant era and yet still expresses the Eternal
Law of God albeit in its specific Mosaic and Pre-Christ form - can it nevertheless
be utilised by Christians to point out and expose sin?
The answer is 'yes' in every way. I have no dispute with the
Decalogue. How could I? It's the very Word of God. And yet it's part of the
Word that has been fulfilled and thus is no longer authoritative as it stands. It must be read in light
of the New Covenant. If this is done we can go back and glean lessons and
imagery from it to be sure but we don't take it as a positive standalone
portion of Scripture that we then apply universally to a non-covenanted world
and divorced from the expansive teaching of the New Covenant.
Again, this is the folly and serious error of posting it on
public buildings and in classrooms and courtrooms. That is to decovenantalise
it and fails to read it in the New Testament context.
Sin is sin and we can point to the commandments that people
break in order to convict. Paul does this in the epistles. But at the same time
as New Testament Christians we should understand that righteousness and
obedience are far more profound and even demanding than what is revealed in the
Decalogue. We are called to a higher calling than merely 'thou shalt not'.
We can even utilise the Sabbath as a means to convict though
its use will certainly be more nebulous and difficult to understand. Though
there is no Sabbath (properly speaking) in the New Covenant, the core of the
command dealt with concepts such as time given to God, worship, preparation for
heaven and so forth. It's something that might resonate say with someone that's
a workaholic (in the sinful sense) – or someone that is godless in their time
and energies.
The Decalogue still has utility as does the whole of the Old
Testament. The problem today is the way in which it is used, the way in which
the Old Testament is sometimes put on equal footing with the New Testament.
Some have done this deliberately as a kind of counter to Dispensationalism. I
can appreciate their desire to counter Dispensationalism's over-emphasis on absolute
and near-absolute division but we needn't respond to their extreme position
with an equally extreme view oriented the other direction – with a Judaized hyper-emphasis
on unity.
The New Testament has priority and it fulfills and interprets the Old. The Old Covenant is technically and even functionally obsolete and as it is revelation from God it is still potent, but it would be not only foolish but wrong to read it apart from the lens of the New Covenant. This violates certain canons of interpretation within some sectors of the academy but they're wrong in their approach. The Bible is not like other books. It's not merely a collection of antique writings that have been cobbled together. Providence and the Spirit forged the book – that which we rightly call the canon. The book does not belong to the academy. It is the province of the Church alone – and though seem erroneously deem it anti-Semitic to say so, that's also true of the Old Covenant. The Jews forfeited their covenant right to it when they rejected Christ – its very heart, theme and central subject.