After decades in public life, at the age of 59, Kamala Harris is doing something that many younger, greener professionals lack the humility and discipline for.

She’s growing, right before our eyes. She’s learning, in the nick of time. And her acceptance speech on Thursday night was a hopeful, heartening tribute to that education, the speed and thoroughness of which could determine whether this country is spared a second, ruinous dance with Donald Trump.

I used to get the sense that nerves flattened Harris’s effervescence and doubts obscured her luminescence. She has the gift of radiance, but she hasn’t always embraced it.

She embraces it now. She walked to the microphone at center stage in Chicago with a smile as uncontainable as it was undeniable. That megawatt mien has become her superpower. And she has wised up enough to know and take full advantage of it.

She used to struggle somewhat to capture the emotion and mine the meaning of her life story. But she told it with naturalness and charm, dwelling on the most relatable details, including her mother’s advice. “She also taught us — and never do anything half-assed,” Harris said. “And that is a direct quote.”

She explained, clearly and bluntly, why she became a prosecutor and what she took away from that job: “I believe everyone has a right to safety, to dignity and to justice.”

She defined the peril that Trump poses without sounding gleeful or puerile, without conflating the parts of him that are merely ugly with the ones that are truly dangerous, without being or sounding, well, anything like him. Elections are about contrasts. She presented a stirring one.

A succinct one, too. Her remarks were less than half as long as Trump’s at the Republican National Convention, where he rambled to an all-time convention-speech record of more than 90 minutes.

Too succinct? It was a speech that, like her presidential campaign to this point, was heavy on principle and light on specifics. It stated goals more than it laid out plans. But there was sense to that. Detailed prescriptions aren’t grist for memorable oratory.

There was even more sense to some of what she carefully included. She methodically addressed what critics have identified as possible vulnerabilities. The southwestern border? She marched straight to it. Israel? She spoke up for it — while also taking care to decry Palestinians’ suffering and refer to their right to self-determination. The gravitas and knowledge for a large presence on the global stage? She discussed world affairs in a strong, confident voice.

And she didn’t dwell on identity but repeatedly emphasized unity. That’s the right strategy for a general election in which voters in the middle may decide the winner. It’s the right prophylactic against Republicans’ casting of her as a “communist.”

And it reflected another crucial difference between the Harris of the past and the Harris of the present. The new version has improved judgment. There’s no overstating how much rides on that.