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.