The contest is expected to generate revenues of over £160 million.
Filipino Pacquiao is considered the top competitor of his generation and has previously spoke of his Christian faith.
"I have a lot of dreams and visions," he told the Guardian, "I even heard the voice of God. When I heard the voice of God, I am trembling and melting. I feel I have died. It was an amazing, amazing experience.
"I'm happy because I found the right way, salvation, born again. We are required to be born again, all of us.
"Christ said unless we are born again we cannot enter the kingdom of God. So it's very important to me.
"Jesus Christ said: 'I am the way and the truth and the life. No one comes to the Father except through me.' There is no other way. The only way is through Jesus."
The boxer had been seen as the 'bad boy' of the sport until a few years ago.
"People are surprised by the way I have changed my life," he said.
"I knew I could do whatever I wanted. But I changed when I heard the voice of God, and I can testify that there is a God.
"I saw two angels, white, long, big wings. I saw Paradise. God showed me about the end of time. This all happened within the last three years. That's how I changed my life."
Pacquiao, an eight-division world champion, and Mayweather, unbeaten after 47 professional fights, have long tried to agree a deal.
The fight has now been set in stone and will take place in May
Pacquiao said: "I am very happy that Floyd Mayweather and I can give the fans the fight they have wanted for so many years.
"They have waited long enough and they deserve it. It is an honour to be part of this historic event. I dedicate this fight to all the fans who willed this fight to happen and, as always, to bring glory to the Philippines and my fellow Filipinos around the world."