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The Mets are about to receive a significant jolt, with six-time All-Star J.D. Martinez set to join them for the series opener against the Cardinals. More than a month after inking Martinez to a $12 million contract, the Mets recalled him from Triple-A Syracuse on Friday and plugged him immediately into their lineup.

“He’s a professional hitter,” co-hitting coach Jeremy Barnes said. “He’s one of the best in the game. He could probably be a hitting coach in his own right.”

While Martinez won’t transform the Mets overnight, he should add considerable length and heft to manager Carlos Mendoza’s lineup card. Here’s everything else you need to know about Martinez’s debut:

What took Martinez so long to join the Mets?
Multiple factors were at play here. One of several Scott Boras clients who didn’t sign until well after Spring Training began, Martinez agreed to terms with merely a week left in camp. He consented to open the season in the Minors, where he could ramp-up to game speed.

The original plan was for Martinez to debut on or around the date he was first eligible, April 7. But he subsequently began experiencing back stiffness, necessitating a cortisone shot to reduce the inflammation. It’s the same injury that cost him time last April, and on Martinez’s recommendation, the Mets opted to treat it the same way the Dodgers did.

Following a shutdown period of a little less than a week, Martinez began swinging a bat again. He then played in three Minor League games, which were his final hurdles before activation.

How did he perform in the Minors?
The most applicable answer to this question is, “It doesn’t matter.” Martinez’s ramp-up was essentially a condensed Spring Training, and it wouldn’t be wise to read any more into it than a typical Grapefruit League stat line. It was also an extremely small sample size. But for the curious, Martinez slashed .316/.381/.421 with two doubles and four RBIs over two games at Triple-A Syracuse and three at Single-A St. Lucie.

Of note, Martinez put six balls into play at exit velocities over 100 mph (including two at 109 mph at Syracuse), suggesting his bat speed is right where it needs to be.

What position will Martinez play?
Designated hitter and likely nothing else. Since joining the Mets, Martinez hasn’t taken any outfield reps. Although he appeared in three games in left for the Dodgers last season, Martinez has mostly been a DH since 2018. The Mets may eventually have Martinez take practice reps to keep him fresh for an emergency, but he won’t spend any significant time in the outfield.

Where will he hit?
Although Mendoza hinted this spring that Martinez would bat cleanup, Starling Marte’s resurgence has created a clear Top 4 of Brandon Nimmo, Marte, Francisco Lindor and Pete Alonso. At least initially, Martinez will bat fifth after Alonso.

Whose roster spot will he take?
The Mets announced that infielder Zack Short was designated for assignment to make room for Martinez on the roster. Short is a talented defensive infielder, but he had a limited path to playing time -- especially because he thrives in a lot of the same areas as infielder Joey Wendle, who’s on a $2 million guaranteed contract. The other candidate, DJ Stewart, can still find playing time as a left-handed complement to Martinez. Manager Carlos Mendoza said that early on, Martinez will require regular maintenance days.

"Tough one," Mendoza said. "Not an easy decision, obviously because of who [Short] is and what he's done. He's done everything we've asked him to do."

What kind of player is Martinez?
On the field, his reputation is stellar, with six All-Star appearances, four Top 25 MVP finishes, nine seasons of 20-plus homers and three Silver Sluggers. His peak years from 2017-18 were spectacular, with a combined .319/.391/.655 slash line, 88 home runs and 234 RBIs.

Off the field, former teammates have described Martinez as one of the most knowledgeable hitters in the sport. Mets officials are intrigued by the types of intangibles he could offer developing players such as Brett Baty, or even accomplished veterans like Alonso and Lindor.

“I have heard that he’s a freak when it comes to hitting,” Lindor said. “I love that. I can’t wait to see how he goes about his business.”

How have Major League hitters like him fared at age 36?
Players, especially position players, are well into their aging curves by their mid-30s, resulting in more regular injuries and dampened production. Martinez has already experienced a bit of that, averaging only 126 games per season the past two years despite serving almost exclusively as a DH.

But it’s also far from unprecedented for upper-30-somethings to rake. Over the past decade, 11 players 36 or older have produced seasons of at least 20 homers and an .800 OPS, including Nelson Cruz (four times), David Ortiz (three times) and Justin Turner (twice). It’s a bit of an adapt-or-die scenario; few hitters who’ve managed to stay in the Majors at such an advanced age have been downright bad. These tend to be the stars of the game.

It’s impossible to tell when a player will fall off the aging cliff, but there’s little reason to believe Martinez is in imminent danger of doing so at 36.

(For what it’s worth, Martinez won’t be the oldest player in the Mets' clubhouse. That distinction goes to reliever Adam Ottavino, who has had a stellar April at age 38.)

How has Martinez fared against this weekend’s opposing pitchers?
It’s a mixed bag. He’s 1-for-3 with a homer against Friday’s probable starter, Miles Mikolas, 4-for-10 with a homer off Sonny Gray and 3-for-23 against Lance Lynn.