The Filipino southpaw decided to change his ways after narrowly retaining his WBO welterweight title with a controversial majority decision over Mexican Juan Manuel Marquez in Las Vegas in November.
Roach described that bout as the first bad night Pacquiao had experienced in a decade and that his fighter's preparation had been adversely distracted by his extravagant interests away from the ring.
"Basically all those distractions caught up with us in that last fight," the bespectacled Roach told Reuters at the Wild Card Boxing Club on Monday before conducting a sparring session for Pacquiao.
"In the end, we had a bad night ... our first bad night in 10 years ... and it was time for a change otherwise his career was going to be over. So he made those choices and to me they are all very good choices.
"Manny has got rid of a lot of distractions in his life and he has some new distractions that are a lot better than the old ones."
Asked to detail the distractions, both old and new, Roach replied: "The news ones are a lot of bible study and a lot of praying, and those are not so strenuous a task.
"He gave his nightclub away, he gave his casino away, he doesn't gamble anymore and he doesn't drink any more. He and his wife are together all the time now and they are very happy together.
"Before, he had a ton of distractions that were mentally very tasking on him. Now he is just praying, he's gone back to the bible and it's working out very well for him. He seems like a happier and nicer person."
Pacquiao, who has won world titles in an unprecedented eight weight divisions to cement his status as the best pound-for-pound boxer, said his decision to 'clean up' his lifestyle had been an easy one to make.
"I just want to focus on my career, focus on praying and follow the commandments of God," the 33-year-old said.
"No more gambling, no more drinking. Reading the bible is to know the bible, and I believe that the bible is the manual for life."
For Roach, there has been only one boxing setback since Pacquiao opted to spend more time studying his bible.
"Manny said to me 'God doesn't want me to hurt people', but I told him that God understands that this is a sport, it's the oldest sport in the world and I think he (God) boxed, too. I might be lying a little bit there, but who knows," smiled Roach.
Pacquiao returned to Los Angeles on Saturday, having spent four weeks in the Philippines training for his June 9 bout in Las Vegas with undefeated junior welterweight champion Timothy Bradley of the United States.
While Roach believes Bradley is a challenging match-up for Pacquiao, he forecast a victory inside the distance for his own fighter at the MGM Grand Garden Arena.
"I think Bradley will come after us and I think he will be overwhelmed by Manny's speed and power," said Roach, a shrewd tactician who has been uncannily accurate with his fight predictions in the past.
"But he has a good chin and he's a very tough guy. He's very disciplined and his work ethic is really, really good. It's going to be a great fight as long as it lasts."