WASHINGTON -- Interviewed by The New York Times during the 1960 Democratic National Convention, an unnamed 10-year-old boy spoke for generations of convention spectators: "You know, this is really very boring -- but somehow, you aren't bored."

The politics of any political convention is interesting for only the briefest of moments. Leading into the 1960 convention, Eleanor Roosevelt publicly hoped that John Kennedy's "unselfishness and courage" would lead him to accept the vice presidency where he could "grow and learn." The novelist Gore Vidal contributed an unused draft of Kennedy's convention speech. Sammy Mysels -- the composer of "Mention My Name in Sheboygan" -- co-wrote the Democratic campaign song.

But the right convention speech can transcend the trivia -- and Kennedy had a talent for injecting significance into a political moment. After almost 50 years, the New Frontier remains a vague concept, having something to do with the rising generation that fought World War II and the coming burdens of the Cold War. But the speech lent the young senator a gravity that comes with sternness, promising "more sacrifice instead of more security."

Once again we are hip-deep in convention politics, and Barack Obama has no shortage of tactical advice: Peel the bark off John McCain. Deal with "bread and butter" economic issues. Abandon all this gauzy "rhetoric." And Obama seems to have embraced the conventional wisdom: "I'm not aiming for a lot of high rhetoric," he said Monday. "I'm much more concerned with communicating how I intend to help middle-class families live their lives. ... This is going to be a more workmanlike speech."

That would be a blunder of historic proportions, precisely because Obama has been given a unique historical moment. He will fill it with significance or eventually be filled with regret.

Obama is advised to emphasize middle-class economic themes, as all recent Democrats have done. But to make a speech that will outlive the moment, he should also address America's deeper divisions based on wealth and opportunity, rooted in slavery and segregation, hidden behind highway sound barriers, revealed in crises such as Katrina, forgotten in a politics where only the middle class seems to count. Inequality is inseparable from liberty in a society that rewards striving -- but inequality becomes morally unjustifiable in the absence of economic mobility. America cannot accept the existence of a permanent underclass without altering its defining ideals. If Obama doesn't confront this reality -- given his background and aspirations of unity and justice -- it is hard to imagine that it will ever be confronted.

In his speech, Obama should deepen his arguments about the essential public role of religion and deliver his party from its recent secularism. Religious values should not merely be tolerated out of politeness; they are, in American history, inseparable from the search for justice. They assert a divine source of human dignity -- a firm basis for human equality -- that no law or tyrant or prejudice can erase.

And to give a memorable speech, Obama must find some way to reassert his initial theme of national unity, recently drowned out by the daily gunfire of presidential politics. Every good convention speech includes clever partisan barbs (as did Kennedy's New Frontier speech). But if Obama does not distinguish himself for his post-partisan unity there is little positive justification for his candidacy. And this emphasis is needed, in a country sickened by its own blogged bitterness. Democratic nations are designed for disagreement. They are weakened by contempt. Loyalty to America, at some level, demands loyalty to one another. Love of country requires a regard and affection for our fellow countrymen.

Obama can make all these points with added power because he is part of a great moral story involving aspiration, faith and the struggle for unity. It is the story of lives and wages stolen by fraud and violence, of families broken at the auction block, of millions who died with their hopes unfulfilled, of millions who never abandoned hope. The story of self-evident truths greater than the flawed men who put them to paper, and of courageous men and women who claimed those promises in fact and in law.

This is the reason I will set my sons before the television set to watch Obama's speech. Because it is not "some men" but "all men." Because a historical journey that began in the Middle Passage can end in the Oval Office. Because a "dream deferred" can be fulfilled.

Obama should not underestimate his moment -- or squander it.