It’s that time of year again, and we don’t mean the NFL postseason. Yes, Martin Luther King Day is upon us.

As many Americans know, the King commemoration is an unusual holiday in a number of respects. It’s one of only three federally authorized celebrations of individuals, the others being Washington’s Birthday and Columbus Day. It’s the newest US holiday, created in 1983. It’s been bolstered for 2012 by the opening of the new King memorial on the National Mall in Washington.

But here’s something many citizens may not know: It is really two holidays in one.

There’s the overall King Day, set in ’83 when President Reagan signed a bill putting it in federal law. And there’s the Martin Luther King Jr. Day of Service, established when President Clinton signed the King Holiday and Service Act of 1994. King Service Day is meant to be a day of personal action in Dr. King’s memory on or near his holiday – as its boosters say, a day on, not a day off. It’s promoted by the Corporation for National and Community Service, a federal agency that also runs AmeriCorps and similar initiatives....