For me, the book above all underscores George Washington's greatness, a greatness that didn't stem from any native ability or genius. A bit from the end of McCullough's book underscores this:
Of all the officers who had taken part in the siege of Boston [at the end of 1775], only two were still serving at the time of the British surrender at Yorktown [in 1783], Washington and [Nathanael] Greene...In an interview with Charlie Rose recently, McCullough pointed out that Washington was a "political general" in the best sense of the term. He never forgot that he was a commander subordinate to elected political leaders and that the cause of America was the fight for political freedom. He saw the cause of liberty as being bigger than himself. And he ultimately was, as historian Garry Wills has said, the greatest political leader in human history.
Financial support from France and the Netherlands, and military support from the French army and navy, would play a large part in the outcome. But in the last analysis it was Washington and the army that won the war of American independence. The fate of the war and the revolution rested on the army...And it was Washington who held the army together and gave it "spirit" through the most desperate of times.
He was not a brilliant strategist or tactician, not a gifted orator, not an intellectual. At several crucial moments he had shown marked indecisiveness. He had made serious mistakes in judgment. But experience had been his great teacher from boyhood, and in this his greatest test, he learned steadily from experience. Above all, Washington never forgot what was at stake and he never gave up.
Washington was, of course, an imperfect human being. While later in life, he would see slavery as both a wrong and a doomed institution, he didn't free his slaves during his lifetime, waiting to do so in his will. (Something which Thomas Jefferson, the supposed advocate of freedom, didn't do. This is just one of many of a catalog of Jefferson hypocrisies, all of which add up to his being the most overrated of the Founders, so far as I'm concerned.)
In addition to showing us what the war was like for ordinary soldiers in that first critical year of America's fight for freedom, McCullough also helps us to see why Washington, their leader, deserves to be much more studied and emulated by our school children, citizens, soldiers, and politicians today.