The first part of the Cubs roster moves were easy to understand — adding a pair of pitchers to replace injured arms.

The reasoning behind the third roster move wasn’t quite as clear at first glance.

On Tuesday, the Cubs designated veteran Garrett Cooper for assignment and recalled first base prospect Matt Mervis.

Cooper had appeared in 12 of the Cubs’ first 22 games and performed well — .270/.341/.432 slash line (.774 OPS) with a homer and 6 RBI.

But with Patrick Wisdom back in the fold, the Cubs felt like they had a redundancy on their roster. So they opted to part ways with the 33-year-old Cooper.

Wisdom returned from injury at the start of the current homestand after missing the first several weeks of the season with a back issue.

“The thought was just kind of similar players on the roster,” Craig Counsell said. “And then we’re entering a stretch that we’re going to face a lot of right-handed pitching. So we decided to bring in a left-handed bat.”

Barring a change to a team’s rotation, the Cubs are facing only right-handed starting pitchers over the next week against the Astros and Red Sox. They will likely face at least one lefty against the Mets in New York but then the ensuing series are the Brewers and Padres, who currently have only right-handers in their respective rotations.

Cooper was mostly playing first base and DH — two spots Wisdom could play against southpaws. Wisdom has more recent experience than Cooper in the outfield, where the Cubs also have the right-handed-hitting Alexander Canario available.

Michael Busch is off to a great start at first base and will see the vast majority of playing time against right-handed pitchers. But he also can play all over the infield if a need should arise somewhere else and Mervis’ arrival gives the Cubs another left-handed bat at either first or DH.

Mervis got out to a strong start to the campaign in Triple-A, hitting .288 with a .402 on-base percentage and .606 slugging percentage — good for a 1.009 OPS in 18 games. He collected 5 homers and 6 doubles to go along with 13 RBI in that span.

The 26-year-old slugger struggled in his first taste of the big leagues last season. He hit just .167 with a .531 OPS in 27 games before he was optioned down to the minors in mid-June. The Cubs never called him back up to the majors last season.

“He’s swinging the bat well,” Counsell said. “He’s a hitter. That’s what his trademark is. A normal first stint in the big leagues where it didn’t go necessarily the way he wanted.

“I think it’s a little different this time, hopefully. One, he’s got the experience of that to help him and it’s a little different spot — the expectations are a little different maybe. This is a bat for right-handed pitching that we think we can put him in some good spots.”

Mervis has proven he can succeed in the minor leagues and now gets another chance to show what he can do in “The Show.”

While there were some swing changes he wanted to make in the offseason, Mervis’ main takeaway from his time in the big leagues last year was moving past tough moments more easily.

“Things are going to go poorly,” Mervis said. “They do for everybody. So just being able to flush those when they do happen and move on.

“I think I probably [wore my struggles] a little bit. Probably got in my own way at times overthinking and just not letting the game come to me.”

He was immediately inserted into the lineup Tuesday, hitting 8th and DHing against the Astros. He went 0-for-3 with a strikeout and reached on catcher’s interference in the Cubs’ 7-2 victory.

This time around, Mervis feels like he is in a position to succeed.

“I really like where my mechanics are at, so I’m able to control the zone a little bit better,” he said. “If I can keep doing that, I’ll be in a good spot.”