They think that the 10 commandments and all it's underlying laws, are the highest law that ever was or every will be. Jesus showed a much greater and truer light then Moses.

The law of the LORD is perfect, restoring the soul;
The testimony of the LORD is sure, making wise the simple.
The precepts of the LORD are right, rejoicing the heart;
The commandment of the LORD is pure, enlightening the eyes.
The fear of the LORD is clean, enduring forever;
The judgements of the LORD are true;
They are righteous altogether.
They are more desirable than gold, yes, than much fine gold;
Sweeter also than honey and the drippings of the honeycomb.
Moreover, by them Your servant is warned;
In keeping them there is great reward.

Your throne, O God, is forever and ever;
A scepter of uprightness is the scepter of your kingdom.
You have loved righteousness and hated wickedness;
Therefore God, Your God, has anointed You
with the oil of joy above your fellows.

What the law could not do since it was limited by the flesh, God did. He condemned sin in the flesh by sending his own Son... as a sin offering...

The word "lawlessness", (iniquity KJV) is used to try and communicate a
spiritual ideal to carnal man. A better definition for iniquity is wickedness.

...no doubt can remain that in Romans 13:9 Paul provides us with concrete examples of the law which love fulfils, showing thereby that there is no incompatibility between love as the controlling motive of the believer's life and conformity to the commandments which the law of God enunciates.

The commandments:

You shall not commit adultery
You shall not murder
You shall not steal
You shall not covet

and if there is any other commandment-all are summed up by this: You shall love your neighbour as yourself.

The conclusion is inescapable that the precepts of the Decalogue have relevance to the believer as the criteria of that manner of life which love to God and our neighbour dictates... When Paul says that "love is the fulfilling of the law" (Romans 13:10) it is obvious that the commandments appealed to in the preceeding verse are examples of the law in view. But by the words "and any other commandment" he intimates that he has not enumerated all the commandments.

The distinction is, therefore, that 'the law' is the generic term and the commandments are the specific expressions. Hence, although the apostle John does not speak in terms of fulfilling the law, the emphasis placed upon the necessity of keeping and doing the commandments (1 John 2:3-4; 3:22&24; 5:2&3) is to the same effect. And when he writes that "whoever keeps his word, in him truly love for God is perfected (1John 2:5), he is pointing to what he elsewhere defines as that of which the love of God consists, namely, that "we keep his commandments". The sum is that the keeping of God's commandments is the practical expression of that love apart from which we know not God and our Christian profession is a lie (cf. 1 John 2:4; 4:8).

If the Law is perfect why was anything new needed? Because we couldn't keep it. Not until the Spirit came in power into the lives of Christians following the resurrection of Christ!

I offer this quote from a substantial interdenominational work:

It is false to claim this was not an important issue to Christ. He taught that repentance from all such things were a prerequisite to entering the kingdom of God.

...and if the blind guide the blind, both will fall into a pit."