"It was a letter that was about 'little things' and details," Mattingly said on Monday. "I thought it fit our club perfectly. We're a young club. We kind of made a little bit of a stride last year. We feel like we have the ability to get to that next level. It just pertained to us."
• Read the full letter Mattingly sent to his club
Spring Training opens for the Marlins on Tuesday with pitchers and catchers taking the field at 1 p.m. ET at the Roger Dean Stadium complex in Jupiter, Fla.
Leading into Spring Training, players and staff have been preoccupied in South Florida, taking part in FanFest on Saturday and Sunday at Marlins Park.
• Marlins Spring Training: Schedule | Tickets | Gear
On Monday, it was the final day to relax, and most of the players took to the golf course, participating in the fourth annual Jack McKeon Classic at Crandon Golf Course in Key Biscayne.
It will be all business on Tuesday when it's time for baseball.
In his second season as Miami's manager, Mattingly wanted to make sure everyone involved is in the right frame of mind.
That's where Leyland's letter comes into play.
"This letter came out 29 years ago," Mattingly said. "It's all the same stuff that you talk about every year -- how do you win? The teams that are able to do [little things] are the teams that actually get there. I just thought it was perfect for our club, and I wanted to pass it on."
The Marlins made great strides in 2016. They entered Aug. 1 nine games above .500 and in Wild Card contention.
But in the final two months, they struggled, and the season ended in tragedy, with the death of Jose Fernandez in a boating accident.
Miami finished 79-82.
"The young club window only goes so far," Mattingly said. "You're only inexperienced for some time. This group has been together now [since 2013]. I remember seeing pretty much the same group when I was in the other dugout.
"With a little luck of being healthy and keeping our team on the field together, and us getting better."
They made a few adjustments to their coaching staff. Mike Pagliarulo replaces Barry Bonds as hitting coach. Fredi Gonzalez takes over as third-base coach, and Dean Treanor is the new bullpen coach.
Ed Lucas, who formerly played for the Marlins, is the new administrative coach and video replay coordinator.
"The areas I where think we can get better are our prep and our day-to-day attention to details and the smaller things are going to be the difference for us," Mattingly said. "Can we improve? That's another thing. They make their way through the Minor Leagues, the young guys, because their talent takes them through. When they get to the big leagues, a lot of times they will have some success. But it's the adjustments you make from there, that either take you to a 10, 12-year career, where you're good for a long time, or you kind of get stuck."