CHICAGO -- The Chicago Cubs have been looking for starting pitching in all corners of the league, so when it came via their own backyard it surprised everyone. Team president Theo Epstein was clear as day about why he gave up his top pitching and hitting prospects to acquire lefty Jose Quintana from the White Sox on Thursday.

"It’s an essential step for us to make the most of this window that we have," he told reporters on a conference call. "It's the type of deal we've been looking to make for a long time. It ended up being a surprising dance partner for us, but I think a great baseball trade all around."

Quintana helps now and for the future. That's the beauty of the deal, in the Cubs' estimation. He shores up a current weakness -- the Cubs rank eighth in starter ERA in the NL -- and is under contract through 2020. By then, hurlers like John Lackey and Jake Arrieta might be retired or playing elsewhere. Both are free agents after this season.

"The reality is this was a deal we were looking at over the long haul," Epstein said. "He's just about a perfect fit for us."

Quintana is one of just six pitchers who have thrown at least 200 innings each of the past four years. He has a career 3.51 ERA -- all achieved in the hitter-friendly American League. As for his early-season struggles, which produced a 5.60 ERA through the end of May, the Cubs say they aren't concerned. A scout for another team agreed.

"He may have had a rough time coming off the WBC [World Baseball Classic], when he nearly threw a no-hitter for five innings," the scout said. "He was stretched out too early and that's always taxing. He's been good. He'll be fine."

The only question is whether the Cubs gave up too much. Outfielder Eloy Jimenez ranks fifth on the prospect rankings of ESPN.com's Keith Law, and pitcher Dylan Cease was the Cubs' top hurler in the minors, but that's the price of doing business for an established pitcher, according to Epstein.

"The deal had zero percent chance of happening without Cease in it," Epstein said. "There was no way to make this deal happen without those guys."

Whether the Cubs gave up more than fans would have liked is of very little concern to Epstein, who indicated there is a reason they gave up only prospects in the deal.

"You can read into today's move just how much faith we have in this group of guys," Epstein said, referring to his major league roster. "We own the fact that we had a bad first half, but it's important not to overreact to that."

In other words, the Cubs didn’t want to trade any of the core players who won a World Series last year, or even those who have underachieved so far this season. In Epstein's estimation, the deal will help the Cubs win now, but it doesn't preclude them from winning later, as their base of position players is still very young. Perhaps the Cubs aren't done dealing. At least one decent-looking prospect, switch-hitting corner infielder Jeimer Candelario, wasn't in the trade for Quintana. The Cubs could move him for more pitching before July 31. Moving above the .500 mark -- the team is 43-45 -- at the beginning of the second half would be a good indicator that this season isn't over for the defending champions.

"This deal gives us a chance to step back and survey the rest of the market," Epstein said. "A lot has to do with how we play. We need to play well."