When it comes to inspiration, I often say that passion is everything. A leader simply cannot persuade without it. I write articles offering specific techniques to help you package your ideas more clearly and persuasively, but I can’t teach passion. When you have passion it’s magic and Vice President Joe Biden had it Wednesday night.

By the end of Biden’s remarks at the Democratic Convention, many viewers took to social media to call it of the most passionate speeches they had seen in a long time. A Rolling Stone headline said the fiery speech “brought the house down.” Among the comments on Twitter:

“Awesome speech. I love stuff from the heart with passion.”

“Joe Biden speaks with such passion and energy, I was captivated.”

“I felt Joe Biden’s passion in that speech.”

“Brought me near tears with his passion.”

“Joe Biden’s passion just made the dog jump.”

Look closely at the words in those tweets: heart, captivated, felt, tears. These are emotional words that spark spontaneous applause (and even make a dog jump).

People love to hear people with passion. Harvard researcher Amy Cuddy wrote a bestselling book called Presence, a book about confident body language. The first part of the book has little to do with gestures and posture, and yet has everything to do with it. The first section focuses on passion. “Presence stems from believing in and trusting yourself—your real, honest feelings, values, and abilities,” writes Cuddy. “We tend to put our faith in people who project passion, confidence, and enthusiasm because these traits can’t easily be faked.”

Cuddy writes about a study of 185 venture capital presentations. The strongest predictor of who received funding was not the entrepreneur’s content or credentials. The strongest predictors were “confidence, comfort level and passionate enthusiasm.” Passion came across non-verbally, in the way presenters used their voice, their gestures and their facial expressions.

We know Joe Biden had an abundance of passion for his speech topic because his vocal tone and gestures were genuine and authentic—traits that can’t easily be faked.

When speaking about his son, Beau, who died of a brain tumor last year, he looked up at Beau’s wife and two children. Clearly he had an emotional connection to the words he spoke next:

“But as Ernest Hemingway once wrote, the world breaks everyone, and afterwards many are strong at the broken places. I’ve been made strong at the broken places… We [Biden and his wife, Jill] think about the countless thousands of other people, who suffered so much more than we have, with so much less support. So much less reason to go on. [Biden’s voice gets lower, but more forceful and more intense.] But they get up, every morning, everyday. [Biden’s voice grows louder, he begins to point with his index finger.] They put one foot in front of the other. They keep going. [Biden raises both hands above the waist.] That’s the unbreakable spirit of the people of America. That’s who we are.”

The power of the previous passage comes not from the content, but from the delivery.

The longest and most sustained applause of the Biden speech occurred when Biden criticized Donald Trump. The words he used were common, conversational English and his voice grew noticeably louder as he said:

“He’s [Donald Trump] trying to tell us, he cares about the middle class, give me a break. That’s a bunch of malarkey.”

The applause went on for a full thirty seconds before Biden could go on.

Biden then lowered his voice to nearly a whisper to talk about something he was “deadly serious” about:

“This is a complicated and uncertain world we live in. The threats are too great. The times are too uncertain, to elect Donald Trump as President…”

Biden slowly extended the concluding sentence of the paragraph by adding pauses in between each word:

“We—simply—can—not—let—that—happen—as Americans—period.”

Biden’s voice grew progressively louder as he proclaimed:

“It’s never, never, never been a good bet to bet against America.”

As the cheers grew into a chorus of chants and applause, Biden’s voice grew louder and more forceful, and his pace quickened as he climbed to his conclusion:

“And given a fair shot, given a fair chance, Americans have never, ever, ever, ever, let their country down. Never. Never. Ordinary people like us who do extraordinary things….We never bow, we never bend, we never break when confronted with crisis. No, we endure, we overcome and we always, always, always move forward.”

Biden is so connected to this topic he seems to feed off the applause at the end of his speech, adding words that were not in the transcript: “C’mon, we’re America. We’re America,” Biden shouted as he gestured with two fists pumping into the air.

Biden’s speech worked because he was passionate about the topic. His enthusiasm turned the words into a symphony with a strong start, a moderate middle, and a rousing conclusion.

A speech or a presentation can be beautifully written, but without passion it will fall flat. Presence comes from passion and passion is contagious.