The Chicago Cubs brought on Theo Epstein in Oct. 2011 with hopes that the famed general manager could reverse the fortunes for the “lovable losers,” as he did the “cursed” Boston Red Sox. On Tuesday, Epstein went big and signed one of the best left-handed starters in baseball.

Jon Lester agreed to a six-year deal worth $155 million, in what could be the most lucrative signing for a free-agent pitcher this offseason. The 31-year-old is coming off his strongest season since 2011, throwing nearly 220 innings and with a 2.46 earned-run average with the Red Sox and Oakland Athletics. The Cubs immediately received a boost from Las Vegas by adding Lester. The Cubs’ odds of winning the World Series jumped from 18-1 to 12-1.

Adding Lester was another bold offseason move for a team that had recently hired manager Joe Maddon away from the Tampa Bay Rays, which eventually led to an investigation into tampering. The Cubs also traded for Arizona Diamondbacks catcher Miguel Montero, who is owed $40 million for the next three seasons. Montero finished eighth among catchers in slugging percentage (.370), while being highly regarded for his defense.

It seems that Epstein and ownership have made a more determined effort to make the Cubs a legitimate contender. It’s a shift that many saw coming after years of losing. The team hasn’t reached the playoffs since 2008, and it’s been over a decade since they last won a postseason series. Only two National League teams recorded fewer than Chicago’s 73 wins in 2014.

But will the changes make a significant difference in 2015? Optimism might be high in the Windy City, but Epstein likely needs to do a lot more to make the Cubs a contender next season.

Lester should strengthen a starting rotation that allowed 3.91 runs a game (No. 21). The Cubs made inroads with their rotation after strong seasons from Jake Arrieta, who collected three votes for the Cy Young Award, and 25-year-old rookie Kyle Hendricks, who had just a 2.46 ERA in 13 starts. However, the back end of their rotation is still questionable.

Despite an improved pitching staff, Chicago’s lineup could hold them back from becoming a real threat in the 2015 MLB season. The Cubs finished last in the National League Central in 2014, and were hindered by a lineup that scored just 614 runs (No. 26). Unless they make a trade, Chicago isn’t likely to add an impactful hitter this offseason, considering most of the top free-agent position players have already signed new contracts.

The Cubs do have some reason to be encouraged by their lineup. The team is led by young players, who have a good chance to be even better in 2015. Anthony Rizzo led the team, with 32 home runs and 78 RBI at just 25 years old, and 24-year-old Starlin Castro led the team in batting average. Meanwhile, Cuban outfielder Jorge Soler is regarded as potential breakout star. Chicago also boasts infield prospects Kris Bryant, Addison Russell, and Javier Baez.

Even if the Cubs don’t make the playoffs, they should continue to improve their win total. Before winning 73 games in 2014, they recorded 61 wins and 66 wins, in 2012 and 2013, respectively.

An IB Times staff reporter contributed to this report.