There are essentially two ways for a team to improve over an offseason. One of the ways is the one that’s most talked about - free agency. It’s easier to project for one thing. Player agreeing to sign a deal is a simple process. It’s obviously more complicated than that, but “I want this player to sign with the Cards” is an easy enough discussion.
Trades are the other way to improve. The Cardinals traded Shelby Miller and Tyrell Jenkins to acquire Jason Heyward one year away from free agency after the 2014 season.