"'All of us face hard choices in our lives," writes Hillary Rodham Clinton in the opening sentence of her blockbuster new memoir. It is not a promising start. But the attention of all the world's many Hillary watchers will quicken a mere four lines later when, listing some of those choices – balancing work and family, caring for relatives, holding down a job – she adds: "Whether to get married – or stay married."

No one who remembers the summer of 1998, when the Clintons' marriage hung in the balance in the wake of the revelations about Monica Lewinsky (who gets no name check in the index), will miss that one, heavy with implication and raw with personal hurt, even now.

On the face of it, the new Clinton memoir is about her four years as Barack Obama's secretary of state from 2009 to 2013. But the book is only ostensibly about the past.

The book might not exist – and it certainly would not be receiving the worldwide attention lavished on it this week – were it not for one particular choice that Clinton faces today. She finally gets to that question more than 600 pages later.

It is the one, she says, that she is asked more often than any other: "Will I run for president in 2016?" And her answer? "I haven't decided yet."

Well, maybe she hasn't. But, if so, this book is a very longwinded way of saying "no comment". This memoir is more likely a sign of what we all kind of know anyway: that Clinton is gearing up for a decision soon and that the overwhelming likelihood is that she is going to run for the Democratic nomination.

On one level, the book is a 600-page job application for a process that will get seriously under way next spring. It's none too subtle subtext is: I'm ready.

The subtler subtext is that Clinton is up to the job. Clinton's account of her four years in Foggy Bottom, home of the state department, is predominantly an account of US foreign policy. It conscientiously works its way through the world's trouble spots, rather as Clinton did during her years of office, during which she visited 112 countries and notched up 956,733 miles of air travel. Asia, China, Burma, Afghanistan, Pakistan, Europe, Russia, Latin America and Africa each get a chapter. The Arab spring and the Middle East get seven more. And there is still time for chapters on climate change, energy policy, disaster relief and digital diplomacy.

It's a comprehensive survey of issues facing America and the world – almost. So it is odd, and disappointing, that the issues underlying WikiLeaks and the Edward Snowden revelations, the former of which happened on Clinton's watch but the latter afterwards, are treated so perfunctorily.

In America one chapter saw the light of day earlier than the others. That one, which was leaked to Politico.com at the end of May, deals with the Benghazi attack in September 2012, when US ambassador Chris Stevens and three colleagues were killed in a terrorist attack on the diplomatic compound in the Libyan city.

The Benghazi issue is a lightning rod of Republican lawmaker critics of Clinton, who blame her and Obama for dropping their guard, so the very fact that this chapter was leaked in advance suggests a smart media operation to get the difficult issue out there early.

All this is consistent with the conclusion that Clinton will certainly run. And so are what to some will be the most important seven words in the book. These come when Clinton reflects on her vote, when still a senator, in favour of the Iraq war. This, more than any other action in her political life, cost her the nomination to Obama in 2008.

But now she writes: "I got it wrong. Plain and simple." She adds that she should have said it sooner, only balking because of the fear of the consequences of saying she had made a mistake.

Those consequences may still exist, even 11 years on. The Hillary haters have not gone away. They are merely, like her, older. Yet any damage from the admission of error will surely be massively compensated by the respect that will follow from the fact she has finally tried to heal the wound of Iraq – plus the fact that, on this at least, she has certainly made the right hard choice.