Apple CEO Tim Cook has a reputation for being an operations genius. He has a reputation for keeping an almost superhuman work schedule. But comparisons to his former boss, Steve Jobs, have kept him from earning a reputation as a great public speaker. 

That's about to change. 

On Saturday, Cook delivered Tulane University's 2019 commencement speech. Cook's content, delivery, and body language brought tears to the eyes of some students in the audience and brought everyone to their feet upon his conclusion. 

I wrote the first book on Steve Jobs and his presentation skills, and I've been watching Cook's public presentations since the day he became Apple's CEO in 2011. Like most speakers, he gets better with every opportunity. And there's one reason why: Cook speaks on subjects about which he's passionate.

Passion and purpose are the qualities that matter most to be a great public speaker. Here's how Cook uses them.

Find your purpose and you'll find your voice

In his Tulane speech, Cook explained that his search for greater purpose in life brought him to Apple in the first place:

I had a comfortable job at a company called Compaq that, at the time, looked like it was going to be on top forever. But, in 1998, Steve Jobs convinced me to leave Compaq behind, to join a company that was on the verge of bankruptcy. They made computers, but, at that moment at least, people weren't interested in buying them. Steve had a plan to change things and I wanted to be a part of it.

In the next paragraph, Cook's voice grew louder as he emphasized the ideas he was passionate about. I've bolded the words that Cook punched in his delivery:

He [Steve Jobs] wasn't just about the iMac or the iPod or everything that came after. It was about the values that brought these inventions to life. The idea that putting powerful tools in the hands of everyday people helps unleash creativity and move humanity forward.

Values drive Cook's passion

I recently spoke to Cult of Mac founder and editor Leander Kahney, who wrote a book about Tim Cook subtitled The Genius Who Took Apple to the Next Level. Kahney told me that Cook is an intensely private man, which explains why he was largely unknown when Jobs named him CEO (although Cook ran much of the company's operations while Jobs battled cancer). As a result, Cook was not considered the charismatic leader people wanted to replace Jobs.

According to Kahney, Cook wasn't trying to be Jobs. No one could be another Steve Jobs, and Cook acknowledged it. Instead, Cook focused on what he could control: becoming the best version of Tim Cook.

In his commencement speech, Cook gave students advice for finding careers that will give them a sense of purpose:

Don't waste time on problems that have been solved. Don't get hung up on what other people say is practical. Instead, steer your ship into the choppy seas. Look for the rough spots, the problems that seem too big, the complexities that other people are content to work around. It's in those places that you will find your purpose. It's there that you can make your greatest contribution.

Great speeches go beyond encouraging words. They pack a punch because the speaker has passion for the topic. So, if you want to be a better speaker, find your passion and build your message around it. That's the Tim Cook playbook.