"In it, 'God said to me my grace is sufficient for you for my powers made perfect for weakness' and I just meditated on that verse all week.
"On that back nine I felt very weak, I felt physically weak, my legs were shaking, but I also felt I had a huge mountain to climb to try to beat the field at the U.S. Open and more than anything it just reminded me of that when I am weak.
"God's powers are made perfect. He'll help me if I ask him too, not necessarily to help me to win, help me to try to execute shots under that pressure.
"We want to honor and glorify God however that looks like. Whether it's winning, surely we want to try and to win, but if it's missing the cut, we want to honor him by our attitudes in the way we treat the other competitors, the volunteers."
It's not just some of the world's best golfers who hold deeply religious convictions on Tour.
Simpson's caddy Paul Tesori is just one of those who believes his life has been revitalized by religion.
Baptized in 2010, Tesori says his whole outlook on life has been transformed -- and that is reflected by his blossoming partnership with Simpson.
"I started to do things to be more obedient to the Lord," said Tesori. "My language changed, we all hang around with the boys, and want to fit in a lot more so one of the first things I changed was my language, to try and be less uncouth.
"If my daughter was watching me, I'd try to think what she would think of me at that time or if Christ was sitting with me there, would he be OK with the way I was acting. Very quickly after that I was fired from a job. I'd never been fired before.
"But in December 2010, the Lord brought me Webb Simpson and since then my walk has got 10 folds better."
While Tesori's faith is a source of great pride to him, he is aware of the skepticism that he encounters in espousing his beliefs.
Describing himself as a "sinner saved by Jesus" on his Twitter biography, Tesori also acknowledges the glamorous lifestyle and materialistic nature of the game opens overtly religious players up to accusations of hypocrisy.
"They look down on me and I definitely think there are a lot of Christians that are like that," he said.
"I know my pastor at my church tells us all the time, 'Look guys we can't be the ones that are complaining, bickering or getting divorced or having affairs, if we're the ones that are trying to call more people into the living.'
"People are going to look at us and say, 'I don't want to be part of that.' "
Faith in sport is nothing new -- the sight of soccer stars crossing themselves on entering the field of play, kneeling to offer prayer or pointing to the sky after scoring a goal is common.
Australian golfer Aaron Baddeley recalls how he turned to the Bible during his first PGA Tour event more than a decade ago after speaking at the Easter service earlier in the day.
"I went out and on the last hole I was pretty nervous," he said. "I quoted Second Timothy 1:7 which says 'God did not give your spirit fear but of power and sound mind.'
"I was quoting that as I was nervous around the putt. I stood there and said, 'This is for you, Jesus,' and knocked it in."
Baddeley's tale is not unusual, and the sight of golfer and caddy standing together and reciting from the Bible no longer raises eyebrows from seasoned spectators.
Sports psychologist Dr. Bob Rotella, who has worked with some of the biggest names in golf for the past 29 years, believes faith helps athletes cope with an "achievement orientated society."
Rotella helped Darren Clarke claim a famous victory at the British Open in 2011 and Keegan Bradley triumph at the PGA Championship in the same year.
"People can feel like if you don't achieve, you're a terrible person or you're a failure," he said.