It's clear from the wide range of review comments that this film is not for everyone. If you don't see the point of education, forget it. But the film raises an issue that for many people is very important today -- just what is education for? -- and answers it on two different levels. Explicitly, "pass it on", which doesn't sound very much. But it's the implicit message that matters, which is that education is essential for giving people confidence and fulfillment, as well as many other things.
The film differs in one significant respect from the stage play which was so successful at the National Theatre. Posner, whom Alan Bennett says had much of his younger self in, no longer ends up as a psychotic loner but becomes another teacher. This changes the balance of the moral, as well as increasing the gay emphasis. Bennett has also excised the puzzling opening of the play in which Irwin is seen as a spin-doctor. Yes, the younger actors were getting a bit old for 18-year-olds by the time the film was made, but the visual settings are splendid, and I'm sure I'm not the only viewer who finds the ending -- in either version -- moving.
If your're remotely interested in why people should learn beyond functional necessities, you should see the film or the play, doesn't matter which. If you're not -- why not?