"We must discover the power of love, the redemptive power of love. And when we do that, we will be able to make of this old world a new world. Love is the only way," he said.
US pastor Michael Curry fired up Britain's royal wedding on Saturday with some passionate oratory about the importance of love that left Britons used to far more traditional royal ceremonies bemused.
Curry, the first African-American leader of the US Episcopal Church, opened his sermon in front of Prince Harry and Meghan Markle in St George's Chapel at Windsor Castle by quoting Martin Luther King.
"We must discover the power of love, the redemptive power of love. And when we do that, we will be able to make of this old world a new world. Love is the only way," he said, quoting the civil rights icon.
With rhetorical flourish, the 65-year-old from Chicago said: "There's power in love. Don't underestimate it. Don't even over-sentimentalise. There is power, power in love.
"I'm talking about some power. Real power. Power to change the world," said Curry, who heads up the US branch of the Anglican church and is renowned as an animated preacher in the US tradition.
Curry also referred to slavery, mentioning the healing power of the spiritual music sung by slaves.
Harry and Meghan after tying the knot
The ancestors of Doria Ragland, the African-American mother of bride Meghan Markle, were slaves. Indeed, her surname is taken from a slave owner.
Outside St George's Chapel, crowds of royal fans reacted mostly with bemusement to live images of uncomfortable-looking VIPs as the sermon went on.
"He's still going on!" one man shouted from the crowd. But reactions on Twitter were far more positive.
"I cannot believe there is a pastor talking about slave spirituals at a dang royal wedding. Hello 21st century," wrote one Twitter user, @kateyrich.
Another, @NappyRaccy, wrote: "Never thought I'd hear Martin Luther King quoted at a Royal Wedding."
"This Reverend just won the Royal Wedding," wrote @nat_sinclair93.
TV presenter Piers Morgan posted a picture of Curry with the words: "My new hero!"
Curry's sermon also featured lighter moments.
"Two young people fell in love and we all showed up," he told the crowd, prompting an outburst of laughter.
As he concluded, he rounded off by telling the couple: "We gotta get y'all married!"