It is a Sunday morning church service in Memphis, and Sister Poindexter slips into a trance. Singing Love is the Key, she spreads her arms, closes her eyes and takes a long, ecstatic look at whatever it is that only she can see. The congregation responds and gets to its feet, applauding and encouraging her with riotous shouts of "Hallelujah!" and "Praise Jesus!".
As the choir and the band swell in number and volume, Sister Poindexter just keeps on singing, still audible over the racket, tearfully inspecting the ceiling and forcing her huge voice heavenwards.
Earlier, I had instructed my friends to restrain me if I started to act strangely. I joked that I didn't want to lose the run of myself - end up speaking in tongues or, worse again, giving away all my possessions - but now I suddenly realise that all nervous wisecracking was over.
If this service continued at this sort of pitch, we were all in genuine danger of being saved there and then. And with the soaring voice of Sister Poindexter filling the church, I discovered, to my shock, that my breath was beginning to catch, that my chest was starting to heave and that I was showing all the early symptoms of bursting into tears. It was a scary moment.
Fortunately, I was suddenly distracted by the real reason I was there. The Reverend Al Green walks in and slips quietly into his seat.
He smiles the broadest of smiles and checks out the faces in his congregation - his mom, his ministers, his flock and the odd white faces from distant parts.
"Where you from?" he beams.
"Who me?"
"Yeah, you! Where you from?"
"Dublin."
"Oh my! Dublin! I love Dublin. I been there! I love it! Let's hear it for Dublin Ireland! Praise Jesus for our visitors from Dublin Ireland! We are blessed with people from Dublin this morning!"
Al Green and his congregation at The Full Gospel Tabernacle are well used to visitors. They welcome us, pray for us - and even though we are the worst- dressed people in the place, we are made to feel very much at home. The church was founded by Green in 1976, and he has been pastor ever since, singing and preaching most Sundays. But visitors should know that this classiest of soul-singers will not be doing his greatest hits, because this is, very definitely, a church.
"I know people come for all reasons," he says. "Some come to see Al, some come to see the Reverend Green - of course they do and I'm glad. I'm honoured and blessed to be in the ministry and I'm so thankful. I've enjoyed every moment of it and I wouldn't take a moment of it back. I'm blessed."
Born in Dansby, a few miles south of Forrest City, Arkansas, Green was singing gospel music from an early age. He first performed with his brothers in a quartet and travelled the Delta gospel circuit and beyond. But when the family moved to Michigan, the young Green soon strayed and began listening to the secular sounds of Jackie Wilson and Sam Cooke.
Inevitably, he did exactly what his heroes had done, taking that treacherous jump into "wordly" music. With his new groups, the Creations and later the Soul Mates, he became a regular on the r 'n' b scene and even scored an early top-10 hit in 1968 with Back Up Train.
A year later, Green met the Memphis bandleader and producer Willie Mitchell, signed to his Hi label and went back to the heart of the Mississippi delta to record some serious soul. Suddenly, Memphis had a new soul star to rival even the successes of Stax, with Green and Mitchell releasing a string of sophisticated hits such as Tired Of Being Alone, Let's Stay Together and I'm Still in Love With You.
But as the 1970s progressed, the gospel side of Green became dominant once more. In 1978, already ordained, he released The Belle Album. It was to be his last secular album for a long time, and it clearly signalled the way ahead.
Addressing his lover, Green begged for understanding with the words, "It's you that I want, but it's Him that I need." And he was serious. Al Green was now the Reverend Al Green, and all musical energies were to be channelled into praise.
Thumbnail sketches often pinpoint Green's moment of conversion as being the "grits incident" - a rejected girlfriend throwing boiling grits over him and then shooting herself. But whatever the tragedy and trauma of that violent scene, Green himself says the crucial moment was the night in 1979 that he fell off the stage and this time "miraculously" escaped serious injury.
This, he says, was the precise moment he decided to give up the secular for the sacred. As he puts it, he began to think that all the praise and glory he had been receiving should really go to elsewhere. For 15 years, he sang nothing but gospel.
These days, he sings everything - both sacred and secular music - and his Dublin concerts of last year were extraordinary celebrations of all sides of Green.
But back in Memphis, church is church, and while he'll tease the congregation with snippets of Love and Happiness, he'll do no more than that. The Lord, he laughs, doesn't want me to sing that kind of thing this Sunday morning.
But he's still Al Green, and no matter what he sings, nobody can touch him for expression and the sheer beauty of that falsetto scream. So I sat there for three hours and listened to extraordinary gospel sounds with even a few country tunes thrown in - I'll Fly Away and One Day at A Time, transformed by that unique sweet and gritty Al Green sound.
As for Love and Happiness, this was neither the time nor the place.
"That song" he says, "is about the love between a man and a woman, and that's good. But this is God's love. And God's love is higher."
So there I was, getting happy in Memphis. The Full Gospel Tabernacle Church and Al Green singing Precious Lord and praying for everybody in Dublin. He preached, he joked, he analysed his Bible word by word, he burst into song, he waved his arms, he hunched over in exhaustion and people shouted "Yessir!" and "Thank you Jesus!"
I don't know whether it was Al Green or God or both - but those three hours at 787 Hale Road certainly lifted the heart and located the soul.
"Open the doors!" says Pastor Green. "Go home! Pour yourself a lemonade! Don't go callin' on nobody! Just stay home! Put your feet up! It's Sunday! And I thank God today!"