The problem is that Gall is bad defensively in the outfield and the only place he can play well at all is first base. La Russa values defense a lot which is why he's been in the minors so long. Fortunately, he benefits from having a 7-time gold glove winning corner outfielder there to help him, and he's put in a lot of work this Spring to look good out there, it looks like it might be paying off.
The Cardinals are lacking when it comes to a right-handed power bat off the bench, so it would benefit them greatly if Gall could improve his defense in the OF and make the team. If he makes it, he could be Eduardo Perez, but I don't expect a lot of fantasy output from him this year. John Mabry is ahead of him on the depth chart for any position he can play, so it would take a few injuries for him to play everyday.