What does "bite" and "quarter-backing" mean in this context?

It's from the first few lines of the foreword to Karl Llewellyn's "The Bramble Bush":

These lectures grew out of an attempt in 1929 and 1930 to introduce the students at Columbia Law School to the study of law. They were privately printed in 1930, and met with reasonable favour. But I found out early that their bite for a beginning law student lies rather in November than in September; and a man's own ideas--especially on perspective and whole view-- change as he gains experience Hence for ten years I planned and worked over a rewrite. Then it slowly became clear that I have no business to rewrite. The young fellow who wrote these lectures just isn't here any more, and the job he did had its own virtue, and I have no right to mess it up with Monday morning quarter-backing which has used two decades in getting from Saturday to Monday morning.

Can someone give me an explanation of, if not some interchangeable words/phrases for, 'bite' and 'quarter-backing' in respect of the above context? Thanks.

"Bite" here seems to mean "importance" or "relevance". It is not commonly used in American English currently (and possibly even at the time it was written).

"Monday morning quarterbacking" is a reference to American football, and a commonly used phrase in American English. It is in reference to the fact that many American football games occur on Sunday, and the quarterback is the main player making important judgment calls during the game. A "Monday morning quarterback" is then someone second-guessing the quarterback's judgement the next day -- usually fans of the team who are disappointed in their team's performance.

By extension, it applies to anyone criticizing a judgment call with the benefit of hindsight. It carries the connotation that the person making the original judgment call was in the better position to do so. Here, the writer is saying that he should not re-write what he wrote many years ago, since his original perspective would be of more use to the reader.