(1)I’m not surprised that you find the following sentence difficult to understand:
An ounce of wisdom is worth more than a ton of cleverness is the first and highest rule of all deeds and words, the more necessary to be followed the higher and more numerous your post.
It’s because it has an abstruse construction that makes it almost a fused or run-on sentence (
“Fused sentences are very serious and annoying grammar violations”), and one that’s made more confusing by inadequate punctuation. This also explains why, as you pointed out, that sentence appears to be using the linking verb “is” simultaneously for no grammatically valid reason.
The first step to unraveling that sentence grammatically is to recognize that its first clause, “an ounce of wisdom is worth more than a ton of cleverness,” is meant to be some rule being quoted verbatim. As such, that whole clause should be set off by a pair of quotation marks to make it a grammatically legitimate part of that sentence, as follows:
“An ounce of wisdom is worth more than a ton of cleverness” is the first and highest rule of all deeds and words, the more necessary to be followed the higher and more numerous your post.
We can see that when that quoted statement is set off by the pair of quotation marks, it becomes a noun form that serves as the subject of the main clause whose predicate is “the first and highest rule of all deeds and words.” In short, from a sentence structure standpoint, there’s actually only one linking verb “is” in that main clause—the one that links that quoted statement to the predicate of the main clause. Structurally, the other “is” doesn’t count because it’s integral to the quoted statement that’s functioning as the grammatical subject of that clause.
Now, these words that follow the first clause of that sentence in question may look like a subordinate clause but it really isn’t: “the more necessary to be followed the higher and more numerous your post. It’s actually a coordinate clause of the first clause, and together they form a compound sentence that normally would read as follows:
“An ounce of wisdom is worth more than a ton of cleverness” is the first and highest rule of all deeds and words, and the higher and more numerous your posts, the more it will be necessary to follow that rule.”
However,to make the statement more concise and punchy, not only was the second coordinate clause inverted but it was also reduced or ellipted—some words were dropped from it, including the coordinating conjunction “and” and the linking verb form “to be”—as follows:
“An ounce of wisdom is worth more than a ton of cleverness” is the first and highest rule of all deeds and words, [and] the more necessary [it has to be] to be followed the higher and more numerous your posts.”
For an explanation of how ellipses work, click this link to
“Understanding the advanced grammar of elliptical sentences.”(2)Yes, a noun applied between the comparative “more ... than” is grammatically correct, as in the case of “veneration” in this sentence you presented:
For guesses and doubts about the extent of his talents arouse more veneration than accurate knowledge of them, be they ever so great.
The comparison being made is, of course, between two subjects, “veneration” and “accurate knowledge of (the extent of his talents).” But I don’t think inversion has been done to that sentence. What happened is simply that the adverbial modifier “be they ever so great” was moved to the tail end of the sentence for greater impact. The normal position of that adverbial modifier is as follows:
For guesses and doubts about the extent of his talents, be they ever so great, arouse more veneration than accurate knowledge of them.
(3)Regarding the use of the verb “be” after the noun “he” in the following sentence:
“No one must know the extent of a wise person's abilities, lest he be disappointed.”
The word “lest” is being used in that sentence as a subordinating conjunction that means “so as to prevent any possibility, and “lest” is a subordinating conjunction that requires that particular clause to be in the subjunctive mood, which in turn is a form that requires the linking verb “is” to always take the subjunctive form “be” regardless of whether the subject is singular or plural (
“The proper use of the English subjunctive”).