Read it through once

With respect to the mysterious part of the letter, where he speaks of one word which would be of such infinite importance, it is difficult, if not rather utterly impossible, to explain it by any rational conjecture. Mr. Macpherson's favourite hypothesis, that the Prince of Orange had been a party to the late attempt, and that Monmouth's intention, when he wrote the letter, was to disclose this important fact to the king, is totally destroyed by those expressions, in which the unfortunate prisoner tells his majesty he had assured the Prince and Princess of Orange that he would never stir against him. Did he assure the Prince of Orange that he would never do that which he was engaged to the Prince of Orange to do? Can it be said that this was a false fact, and that no such assurances were in truth given? To what purpose was the falsehood? In order to conceal from motives, whether honourable or otherwise, his connection with the prince? What! a fiction in one paragraph of the letter in order to conceal a fact, which in the next he declares his intention of revealing? The thing is impossible.