Why did Bertrand Russell care so much about the meaning of the word "the"?

This post is a letter to my 19-year old self, sitting in a "Philosophy of Logic and Language" lecture, and wondering whether I've made a terrible mistake. "I would give the doctrine of this word" writes Bertrand Russell "if I were dead from the waist down and not merely in a prison." You begin to wonder if being in prison (and so having nothing better to do) is a pre-requisite for caring this much…