By Jim Boulden, CNN

(CNN) -- In a stirring royal wedding address, the African-American leader of the Episcopal Church quoted Martin Luther King Jr. and spoke passionately about the power of love.

"We must discover the power of love, the redemptive power of love," said the Most Rev. Michael Curry, echoing the words of the civil rights leader, continuing: "And when we do that, we will make of this whole world a new world. But love, love is the only way. There is power in love. Don't underestimate it. Don't even over-sentimentalize it. There is power, power in love."

Curry delivered the address shortly before Prince Harry and Meghan Markle -- now the Duke and Duchess of Sussex -- said their vows. He is America's first African-American leader of the Episcopal Church and an avid campaigner for social justice and racial equality.

Curry used King's quote as inspiration for his address, which he used to convey a celebratory message about love. "There's power in love to lift up and liberate when nothing else will," he said. "There's power in love to show us the way to live."

"Dr. King was right," he said. "We must discover the power of love, the redemptive power of love. And when we discover that, we will be able to make of this old world a new world. Love is the only way."

Delivered with Harry and Meghan -- and the rest of the royal family -- looking on, the impassioned speech was one of several standout moments from the ceremony, breaking with the usual somber atmosphere and traditional music and language used in previous royal weddings.

Shots of the guests revealed looks of surprise and amazement -- not least when Curry addressed them directly, asking "Anybody get here in a car today?"

The reaction was even more marked among social media users.

"Bishop Curry is the liveliest priest to ever hit St George's Chapel and the Brits are legit looking frightened," wrote writer Gloria Fallon.

UK Labour politician David Lammy wrote, "Love, Justice, Poverty, MLK, Fire and Slavery in one sermon from Bishop Curry. Amen brothers and sisters, Amen."

King's daughter Bernice expressed her delight at the use of the activist's words in a tweet. "#MLK quote at the #RoyalWedding," she wrote. "Your life, teachings and words still matter so much, Daddy. Congrats, Harry and Meghan!

Rev. Curry rose to fame in 2012 when his sermon "We need some crazy Christians," went viral and was turned into a book.