Q: Use of Past Perfect in Leo Rosten's "O Kaplan! My Kaplan!" An excerpt from Leo Rosten's "O Kaplan! My Kaplan!":

"Excellent... And now, class, let me take one moment to note that there are certain exceptions-"
Groans instantly greeted the ominous 'exceptions'. The beginners' grade had long ago learned to fear - nay, loathe - the Exception to the Rule. It was the bane of their learning, a snake in the garden of perception. (Mr. Krout, the seniour instructor in the ANSPA, once enlivened a faculty meeting by declaring that 'the very bete noir of English is the skulking multitude of Exceptions to the Rule!' How Mr. Parkhill had admired the way Mr. Krout had put that! He admired it almost as much as he admired Mr. Robinson, the school principal, for responding: 'I heartily agree, Mr. Krout. There are as many exceptions to the rule in English as there were thieves in Baghdad!' Who could forget such a simile? 'But we cannot change the rules of grammar - nor, if I may say so, can we exile all the exceptions... Carry on! That is what we all must do. Carry on!' If there was one quality Mr. Parkhill had inherited from his ancestors, it was the capacity to carry on.)

Why does this Past Perfect appear suddenly and suddenly end? The previous sentence is cast in Simple Past (not "had enlivened"). The next sentence carries on in Simple Past too, in spite of the fact that it tells about the same feeling of admiration.
The sentence stands out from the surrounding parts of the passage by being cast in a "deeper" past. But how can it be "deeper" in the past than the sentence with "once enlivened"?

A: You're right.   The action of "had admired" and "had put" is in the same timeframe as "once enlivened", not further into the past.   
The phrase "once enlivened" is not a perfect aspect construction, but it does have something that marks its timeframe as further in the past than the surrounding narrative.   In this context, the "once" means something like "on an earlier occasion" -- the faculty meeting in question concluded before the students began groaning.   Following this clause, a direct quote is cast in the present tense.   
Even though it's a direct quote and its tense is unrelated to the story, it is an interruption from the timeframe of both the class's groaning and the faculty meeting.   There are two different past-tense frames to which we could return.   The perfect aspect marks that we're leaping back to the timeframe further into the past.   
The admiration began in that further past and continues through to the nearer past that is the narrative's main timeframe.  The shift back to the simple past marks a continuation of the admiration that began during the faculty meeting, as it still existed while the students groaned.
