Nobody expects to win every game. Nobody expects their team to be 162-0 at the end of September. Nobody (with the possible exception of George Steinbrenner) would even entertain the idea. Therefore, having a successful regular season and giving your team any chance at a playoff run means winning series. Taking 2 games of each 3-game set (or 3 of 4) is the key if you want to play in October, especially if your team is part of the NL Central (although I won't delve into that bag of worms just now).
This latest series was an especially important one for the Cardinals. Two out of 3 against the Cubs re-secured the Cards in 1st place of their division, gave the team a win before heading off on an 8-game road trip, and one other thing that I won't mention so as not to jinx it. Hopefully they can use the momentum from the win to build on their lead in the Central. The Redbirds have 4 games in Colorado then 4 games in Milwaukee before returning home. The Cubs have a 3-game set in Cincinnati followed by an off-day and a 10-game home stand.