Orange trees produce oranges

The mistake theologians make in trying to find a place and a reason for the law after the Incarnation and death of Christ is still seeing it in isolation. In their minds there is the law, and there is the gospel.

No. There is the law of Christ. And it's simple. Matthew 22 -

37 Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind.
38 This is the first and great commandment.
39 And the second is like unto it, Thou shalt love thy neighbour as thyself.
40 On these two commandments hang all the law and the prophets.

When you still consider the law in isolation you don't understand this:

The law minus the gospel is demonic.

But the law is good! you protest.

The law as it's wielded by fallen man and fallen angels is twisted, distorted, and turned upside-down.

But surely the law can be wielded in its pure form?

Regenerated and glorified man do not need to wield the law. It's in the Devil's and fallen man's interest to wield the law.

But we must follow the law?

Once regenerated it's in our heart to follow the law. Actually, to live and breathe the law; just as an orange tree produces oranges; not out of a sense of following the rules, but because it's an orange tree.