It's part of a novel, so it has a larger context. The parable is not intended for you, the reader, but for the protagonist of the novel Josef K., who is spending time in a futile effort. I'd say it's basically about futility of seeking unattainable answers, and frustration. But it's probably not meant to be 100% understood, as Josef K. is a confused character full of doubts (like Kafka's characters tend to be), the purpose of the parable is not to dispel his doubts but to entrap him more in the frustration.

I didn’t get it either. Maybe it is the opposite of the Gordian knot story?

https://en.wikipedia.org/wiki/Gordian_Knot

Having worked a large bureaucracy, when we'd sometimes get into some catch 22, I used to quote the line "I am only taking it to keep you from thinking you have omitted anything" sometimes to a friend who also knew the short story, and we'd laugh.

Yes I thought at the start it was about how our expectations of how the law works are at odds with the reality

So the gatekeeper is the system keeping us from Justice - mostly money, but also other less tangible barriers. In theory, everyone gets a lawyer, in practice some people can afford expensive ones.

Then the end twist got me confused.

Excercising your rights is a duty, responsibility and experience that is individual to everyone.

Yes, it was very kafkaesque. (I also didn't get it.)

Keep in mind that the story is actually embedded in Kafka's "The Trial", and discussed by two characters within that story, who have very different views of its meaning.

I think it is very deliberately written to be impossible to "understand". If you think you have found its clear and unambiguous meaning, you're wrong.