Stephen Prothero, a Boston University religion scholar and author of "The American Bible: How Our Words Unite, Divide, and Define a Nation," is a regular CNN Belief Blog contributor.

Equality. That's what today's inauguration was about. And we have Abraham Lincoln and the Rev. Martin Luther King Jr. to thank for it.

President Obama took his oath of office on two Bibles: one used by Lincoln during his 1861 inauguration, the other the “traveling Bible” of Dr. King. And during his second inaugural address, Obama read U.S. history through the words and actions of these two men.

In his Gettysburg Address, Lincoln turned to Jefferson's words in the Declaration of Independence to argue that the United States was “dedicated to the proposition that all men are created equal.” In his "I Have a Dream" speech, King argued that our national commitment to equality demanded that we emancipate ourselves from segregation as well as slavery.

In his second inaugural address, Obama began with an extended quotation from the Declaration of Independence. At least five times he referred to equality as our common "creed." And he repeatedly challenged his fellow Americans to act on that creed - to turn the United States into King's "beloved community" and Lincoln's vision (borrowed from the Constitution) of "a more perfect union."...