During the war our lives were regulated at every turn by the distinction between what was and what was not "essential" for what we used to call the "war-effort". Thus the word essential became very familiar to us, and it remains familiar now that much the same is true of the "economic effort". But we must not allow familiarity to lead us into absurdity. To write "I can only deal with applications of a highly essential nature" may perhaps just be allowed to pass; though it is always better to say what you mean, and in this case what you mean is: "I can only deal with applications from people doing 'highly essential' work". But we must draw the line at:
It is confirmed that as a farmer you are granted high essentiality.
This means, I think, "as a farmer you are high on our waiting list", and that would be a more intelligible thing to say. It is so easy to forget that what has a perfectly plain meaning for the writer may be gibberish to the reader.
It is impossible to approve importation from the U.S.A. unless there is a compelling case of essentiality.
This really means, presumably, "unless it is of something that we vitally need".