Mattis was a mediocre college student. He partied too much and was jailed for underage drinking. But then he discovered the Marine Corps. His new book “Call Sign Chaos,” which he wrote with Bing West and which will be released next week, is purportedly about leadership but really it is a portrait of Mattis’s life-defining love for the Marine Corps.

His prose sings when he describes those times when he was out on some battlefield exercise with frontline Marines. When he is stuck away inside the Pentagon or high up commanding NATO, you feel his longing for their presence.

Mattis reads Roman writers like Marcus Aurelius, but he is no stoic. Decade after decade he is touring some front or another, starting a million affectionate conversations. “How’s it going?” “Living the dream, sir,” is how those conversations begin. He trusts his Marines enough to delegate authority down. He clearly expresses a commander’s intent in any situation and gives them latitude to adapt to circumstances.

Love is a motivational state. It propels you. You want to make promises to the person or organization you love. Character is forged in the keeping of those promises. If, on the other hand, you are unable to love and be loved, you’re never going to be in a position to make commitments or live up to them. You’re never going to forge yourself into a person who can be relied upon.

Mattis’s drive, born of his devotion to the Corps, is his most telling trait. He works insanely hard, propels himself extremely quickly, making himself, every day, a better Marine. Much of the work is intellectual. He thought the second Iraq war was a crazy idea, but when he was ordered to command part of it, he started reading Xenophon and ancient books about warfare in Mesopotamia.