The announcement that the Chicago-born presiding bishop of the US Episcopal church, Michael Curry, a campaigner for LGBT rights and racial justice, would deliver the sermon at Saturday’s ceremony was a surprise, given that he had no previous relationship with the couple, but he was asked to contribute to the service on the recommendation of the archbishop of Canterbury, Justin Welby. Effusive and impassioned, injecting black American heritage into the event, he didn’t disappoint.

Top and tailing his ceremony-stealing sermon with words from Dr Martin Luther King, Curry, the first African American to lead the Episcopal church, preached on the transformative, healing power of love through the spirit of “old slaves in America’s antebellum south”. In freeform, rousing sing-song speech, he entwined the legacy of slavery with African American church traditions and delivered his message into the heart of the British establishment. Members of the royal family were visibly stunned and bemused.

Curry, born in Chicago in 1953, followed in his father’s footsteps and was ordained as a priest in 1978, after graduating as a master of divinity from Yale Divinity School. He has been vocal throughout his ministry on issues of social justice and marriage equality. His decision to refer to Balm in Gilead, an old “Negro spiritual” sung by slaves to invoke the concept of salvation through Jesus was audacious and deliberate. “If you cannot preach like Peter, there is a balm in Gilead. And if you cannot pray like Paul, to make the wounded whole, you can tell the love of Jesus. There is a balm in Gilead, how he died to save us all, to heal the sin-sick soul.”

Curry offered evangelical hope to the great and good gathered in Windsor and black spiritual tradition was liberally quoted throughout. Rather than focus on the couple and their nuptials, Curry called for attention to war, poverty, hunger. “Imagine neighbourhoods and communities when love is the way,” he rallied.

“Imagine governments and nations when love is the way. Imagine business and commerce when love is the way.” In wry self-deprecation, he made the congregation giggle by assuring them he was almost done. “With this I will sit down,” he joked, “we gotta get y’all married.” He then went on to recall French Jesuit priest Pierre Teilhard de Chardin, “one of the great minds and spirits of the 20th century”, in a fiery conclusion urging that “ if human beings ever harness the energies of love, then for the second time in history, we will have discovered fire.”

Welby urged his followers on Twitter to watch the 13 minute sermon in full, describing it as “extraordinary and powerful”.

Prince Harry, sixth in line to the throne, and Meghan Markle, also broke from tradition with their choice of music. Whereas hymns and classical music are the customary fare at royal weddings, the couple asked Karen Gibson to conduct the black gospel Kingdom Choir in a rendition of Ben E King’s Stand By Me. To close the ceremony, the choir undercut the pomp of the service with Etta James’s civil rights anthem This Little Light of Mine.

Facebook Twitter Pinterest The actor Idris Elba and his fiancee Sabrina Dhowre help to adds celebrity glamour to the event. Photograph: Ian West/PA

As the Guardian music critic Alexis Petridis noted: “It says something about how staid and conservative the musical choices at royal weddings tend to be that two pieces of music with a collective age of 104 counts as racy and daring” .

The couple also picked 19-year-old cellist Sheku Kanneh-Mason, winner of the BBC’s 2016 Young Musician award, to perform as they signed the register. Kanneh-Mason, who comes from a family of classically trained musicians, tweeted: “I was bowled over when Ms Markle called me to ask if I would play during the ceremony, and of course I immediately said yes!!! What a privilege. I can’t wait!”

African-American royalty, namely Oprah Winfrey and Serena Williams, were prominent among the guests. Bollywood and US TV actor Priyanka Chopra, George and Amal Clooney, Idris Elba and his fiancee Sabrina Dhowre bought a touch of celebrity glamour alongside seasoned, royally approved guests the Beckhams, Elton John and James Corden.

Twitter buzzed at the gear-change for the House of Windsor. Naomi Campbell wrote: “BISHOP MICHAEL CURRY GIVING ME LIFE” while Ed Miliband claimed that Curry “could almost make me a believer”. TV presenter Angela Griffin summed up much of the mood: “Not sure I’ve ever seen so many people of colour at a royal event ever. Feel quite proud watching with my 10-year-old mixed-race daughter”.