President Obama lays a wreath at the Tomb of the Unknowns in Arlington National Cemetery.

It often seems that Memorial Day was invented by manufacturers of outdoor cooking supplies, and for many Americans — if not most of them — the last Monday in May is only about gathering the family for a barbecue.

There’s nothing wrong, of course, with enjoying the company of people we love in a bucolic and relaxing atmosphere, but it comes as a shock to many people that the holiday’s purpose is to force us to remember the sacrifice of Americans who died for our liberty.

The first Memorial Day was, as Yale Professor David Blight observed, actually created in Charleston, South Carolina, by “Black Americans recently freed from slavery, announcing to the world…what the war was about.”

Most people forget that, in the effort to keep the country together and to destroy slavery, more than six hundred thousand Americans perished.

In the last seventy years, it has become easy to take American freedom for granted. But in the Second World War, not a household escaped being touched by the conflict, and nearly everybody did something to defeat the Axis.

In my neighborhood in New York City, all my friends’ fathers had served in uniform, and many had the horrific scars to prove it. Some of my friends didn’t even have fathers, because they were lost on Iwo Jima or on D-Day or at the Battle of the Bulge.

Two decades after my father returned from fighting in New Guinea and the Philippines, I went to war myself, and I got a chance to see, up close, what the words “service” and “sacrifice” really mean: dear friends and comrades killed and maimed in an effort to keep each other alive.

Because now our armed forces are composed entirely of volunteers, most Americans do not know anyone in uniform, and service is an abstraction. So it isn’t surprising that Memorial Day doesn’t hold the significance that it did at its inception, or after each of the conflicts in which brave men and women have served in the past.

But to keep alive the flame of freedom, we must also keep alive the memory of those who sacrificed so that we can enjoy it. And for every American who has fought against our enemies, there has been a family, just as brave, at home. For every American who has surrendered life in combat, there are many more at home who live without someone they loved.

We should enjoy the holiday, to be sure, but we should not be complacent about the courage it has taken so that we can do it.

Colonel Jack Jacobs, USArmy, ret., is a Medal of Honor recipient and MSNBC/NBC News military analyst. Follow him on Twitter @ColJackJacobs