In the film About Schmidt, Jack Nicholson gives a superb performance as Warren Schmidt, a retired vice-president of an insurance company in Omaha, Nebraska.

After his wife's death, he is forced to confront the meaninglessness of his life.

It is a story of failed relationships and petty betrayals. Schmidt has never made the effort to understand or appreciate his wife and daughter. Only when he loses both, one by death, the other by marriage, does he realise what they meant to him and how little he did to earn their love. It is a painful film, and only laughter makes its intense sadness bearable. Schmidt is a mean-spirited man who discovers he has done nothing to win a place in other people's affections.

That is, until the closing scene. It is here that the writer-director Alexander Payne delivers a master stroke. Throughout the film, he has used a narrative device to allow the central character to think aloud. The one positive thing Schmidt has done in retirement is to answer a television appeal to adopt a six-year-old child in Tanzania by sending a monthly cheque to pay for his treatment. Along with the cheque, he sends a letter telling the boy, Ngudu, about himself. These letters give the film its continuing commentary, allowing Schmidt to reflect with bemused anger on what is happening him.

Only in the final minutes do we discover that this is not just a technical device but the film's entire point. Schmidt is driving home after his daughter's wedding, a match he tried but failed to prevent. Overwhelmed by a sense of failure, he writes Ngudu another letter, his requiem for an inconsequential life.

"I know we're all pretty small in the big scheme of things," he writes. "What in the world is better because of me?...I am weak and I am a failure... Soon I will die... When everyone who knew me dies too, it will be as though I never even existed...What difference has my life made to anyone? None that I can think of, none at all."

Just then he receives a note from Tanzania, from the nun who has been looking after Ngudu. She thanks Schmidt for his cheques and letters, and tells him about the boy. He cannot write, but he has sent Schmidt a drawing instead. It shows two stick characters, obviously the boy and Schmidt. They are holding hands, and the sun is shining. Schmidt slowly realises he has done one good deed after all. He begins to weep, and on that image the film ends.

We know why Schmidt is crying -for the good he failed to do, and for the one decent thing he has done, for a child far away whom he has never met. The scene is that rarest of contemporary phenomena, a moral statement. One act can redeem a life. It is a daring affirmation. One reviewer called it a "trumpet blast of defiant non-irony." But it is a moment of great cinematic and moral power.

The good we do lives after us; the rest is oft interred with our bones. Where today will we hear that truth if not in our religious traditions? The meaning of a life is the difference we make to other people. Schmidt's tears are a sermon without words, reminding us of what so much tends to make us forget: to live is to give.

Rabbi Dr Jonathan Sacks is the Chief Rabbi of the United Hebrew Congregations of the Commonwealth

This article first appeared in Credo in The Times on Saturday October 18, 2003