Bill Clinton's speech succeeded in humanizing Hillary

"Actually doing the work is hard," Bill Clinton said. "You know, it's hard, and some people think it's boring."

That was the key thesis of his long, rambling, strangely compelling speech about his wife Tuesday night. All day, leaks suggested that Clinton was going to give a very personal speech about Hillary Clinton, rather than a wonky, policy-oriented one. And it wasn't a crazy idea. That, after all, is what the nominee's spouse normally does. And Bill is Hillary's spouse.

But I didn't believe he would do it. And of course he didn't do it.

It was the most policy-packed speech so far of either convention, ranging from early childhood education to the role of climate change in American foreign policy and everything in between.

But it was also a deeply personal speech. Because for Bill and Hillary Clinton, policy is deeply personal. David Brooks thinks Hillary should talk more about her hobbies to seem more human. Bill's mission was to make you believe that working to help solve policy problems is her hobby — and a very human one at that.

For Hillary, politics is a vocation. The genius of Bill's speech was to make it seem like a compelling one.

Killing them with details

Bill Clinton has never delivered the kind of speech that's considered "good" by the standards of conventional rhetoric. His genius is a nearly unique ability to make that lack of conventional speechifying work. His opening section, a seemingly endless blow-by-blow account of Bill and Hillary Clinton in the 1970s, was like listening to the most fascinating tedious old man you'd ever heard.

Only Clinton could deliver such a dull text and make it work.

And it really did work. The sheer piling on of different points itself became a kind of point. Even though you know a lot about Hillary Clinton, there's so much more that you don't know.

A lot of it is kind of tedious. Because doing actual things in the actual world to help actual people with actual problems is simply difficult and demanding.

Bill dwelled in a variety of contexts on something that's become unfashionable recently — implementation details. He mentioned that when Hillary urged him to expand Arkansas's preschool offerings, it wasn't just a matter of penciling in a number in a box. There had to be actual schools and an actual model for what the schools should look like. There was a program in Israel that was working well, and a woman involved in setting it up was going to physically transport herself to Arkansas to sit down with them and help set things up. Then when they were up and running, Bill had to visit the school.

Decades later, as secretary of state, Clinton "tripled the number of lives that are being saved around the world with your taxpayer dollars — and it didn't cost you any money."

It didn't cost you any money because the implementation details matter. It's not just how much you spend — it's what you actually do with the money. To be effective, you need to be smart, and you need put in the work.

At last, a speech for blue-collar whites

In its emphasis on the practical, and on the hard work involved in making it happen, Bill Clinton also offered the first major effort of the convention — and in many ways of the campaign — to speak to the white working-class communities that are Donald Trump's main base of support.

These are communities in which the notion that "America is already great" does not resonate, and who aren't inspired by paeans to the growth of American diversity. They're also not, realistically, communities that Hillary is going to win.

But Barack Obama didn't win them either, and he still won two elections in a row. Relative to John McCain and Mitt Romney, Trump is doing worse with white college graduates and nonwhite workers. But the election isn't a blowout for Clinton because he is doing much better with non-college whites than the previous two Republican nominees. Holding those margins to a respectable level would seal the deal for Hillary.

Bill's finest moment was aimed squarely at that constituency:

There are clear, achievable, affordable responses to our challenges. But we will not get to them if America makes the wrong choice in this election. That is why you should elect her. You should elect her because she will never quit when the going gets tough. She will never quit on you. She sent me in this primary to West Virginia, where she knew we were going to lose, to look those coal miners in the eye and say, "I am down here because Hillary sent me to tell you that if you really think you can get the economy back that you had 50 years ago, go for it. That if she wins, she is coming back for you to take you on the ride to America's future."

Will most voters in West Virginia find this compelling? Of course not. But the hope is that enough will. And, more to the point, that some of the people living in the West Virginia-esque parts of Pennsylvania and Ohio and Virginia will, and that therefore Hillary will carry those states.

The pitch is simple: Bill and Hillary Clinton understand that there are big regions of this country that are suffering from big problems. And while Trump is offering pleasantly easy and pleasantly vague solutions to those problems, you probably know deep in your heart that big problems are harder and more complicated than that. Actually doing the work of fixing them is hard. And Hillary Clinton is ready to do some hard work on them.

After all, it's what she's been doing for decades.

And what's Donald Trump done?

Commentary by Matthew Yglesias, a writer at Vox. Follow him on Twitter @mattyglesias.

For more insight from CNBC contributors, follow @CNBCopinion on Twitter.