Based on the parable alone, the Law is simply presented as the place into which one wants entry. With what the story gives us, we have to assume either that the man from the country did everything right and that you just don't get to get into Law but have to wait on a stool, or that he failed to do the thing that would get him in. Like most parables, it seems the parts would apply in cases of varying profundity. There is a specification that I find very interesting, though. The man from the country makes many attempts at entry.
Bribery is named as one instance.
So, there was a specific thing the man wasn't doing. I think once we've determined what that is, we can move on to what the gatekeeper represents etc etc. I've thrown out the hypothesis that he wasn't fighting the gatekeeper. If it was written as a part of it, then we might want to consider viewing it as a part of The Trial. Regardless, I think studying it on its own first is pretty much necessary if we want to look at it as part of The Trial at all.